SECTION III. Diseases of the Blood Vessels

DISEASES OF THE BLOOD VESSELS

The gross anatomy of the blood vascular system is constructed upon the same general scheme throughout mammals and upon a comparable basis in birds. Microscopically there is little variation throughout the orders unless it be in the relative proportion of muscular and connective tissues. The origin of the great vessels at their cardiac base and their distribution to the pulmonary and to the greater circulations in no way differ in these two classes in that it always consists of an efferent pathway to the lung and a root vessel above the aortic orifice. The former has usually quite a distinct origin on the right side, but in some birds the posterior wall of the pulmonary artery may overlie the entire aortic base; this, however, is not the rule for birds. The aorta in most mammals remains a separate and distinct vessel for some distance, after which it gives off the innominate and subclavians. In the birds on the other hand, the stretch immediately above the aortic valve is usually ballooned out somewhat, into a sort of sac or ampulla from which the subclavians and descending aorta arise. This forms a structure of rather trident shape, the lateral prongs being the subclavians, the middle and posterior being the aorta proper. In some birds the aorta may have the length of a centimetre or more then dividing into the left subclavian and right aorta from which the right subclavian comes off.

There is definitely more support to the heart and vascular roots in mammals than in birds, in the latter class these structures lying quite free between the lateral air sacs and well in front of the lungs. Nor is there the richness of mediastinal areolar and fatty tissue in the winged creatures.

The vessels of mammalia retain a considerable wall throughout nearly their entire length. At first the wall is thin compared to the calibre of the vessel while the arteries smaller in calibre, have a heavy wall. In birds the arterial stalk at the heart is supplied with very heavy walls, but after the second branching the relation of wall to calibre seems to continue about the same. In this class the stalk vessels have wall to calibre relation of 1 to 3 (measurements in 2 Passeres, 1 Psittaci, 1 Accipitres) whereas in mammals the relation varies from 1 to 5 to 1 to 7 (observations on 2 carnivores, 1 ungulate, 2 rodents). In mammals the consistency of a normal artery wall remains much the same, a firm, resilient, yellow-white tissue, quite opaque and standing open upon cross section. In birds this description covers the main stalk, the aorta in the abdomen and the first part of the carotid and iliacs. When these characters are lost, the arteries become semitranslucent bluish strands so that they are difficult to follow in the muscles of the neck and extremities. This is particularly true in the Passeres, Picariæ, Galli and Columbæ while in the Psittaci, Accipitres, and Anseres the arteries are distinctly whiter than the veins but yet quite soft. In the Herodiones and Struthiones, thick walled vessels may be followed as far as the second joint in both extremities. These differences depend in part upon the grosser construction of the central arteries in Aves and in part upon the larger amount of elastic tissue in them than in the secondaries and smaller vessels, and than in comparable mammalian vessels.

It is impracticable to go into the minutiæ of histology in the different orders, which indeed varies but little, although attention might be directed to the facts that in all central vessels the relative amount of elastica is greater than in smaller ones and that muscular tissue seems to exceed in the latter. Considerable work has been done upon the amount and arrangement of muscle bands in isolated genera, but no comprehensive data are at hand upon orders. The strands of muscle do not seem arranged so regularly as in mammals; the pulmonary artery of the cat, for example, has a muscle arranged like an oblique band in waves or festoons along the length. The mammals as a class seem more richly supplied with arteries and veins than do the birds, and the square area of the vascular system is likewise larger. This is distinctly different from the amount of heart bulk as given in the discussion of kilogram-heart ratios so that one might say that the birds are “overhearted and undervesseled.”

In so far as the physiology of the two classes is concerned it is obvious that a different regulatory system is necessary because, aside from the variations of pressure incidental to pulmonary, muscular and visceral work, there remains the altering pressure within the air sacs of Aves, a force different under states of rest, of running, of deep water swimming and of flying with or against the wind. Part of the internal air pressure variation is cared for by the ability a bird has to respire the air in its sacs and bones, but in prolonged exposure to the pressure under water or during protracted flight some compensatory mechanism doubtless exists. This seems to reside in part in the heavy elastic quality of the arterial stalk and the very rich venous supply of the abdomen, including the renal-portal system and the distensible pelvic veins. Just where the governing power for this mechanism resides is as much a matter of debate as in the case of the human being, but certain researches would place it in the caudate lobe and pituitary body.

Having discussed these general comparative data we can now pass to a consideration of the pathology seen at this Garden. The subject will be studied from the standpoint of the vessels as a system and the changes peculiar to it. Naturally the most important lesions affect the great stalks and the principal trunks, from which the processes may continue into the smaller vessels. The essential alterations are inflammatory and degenerative, of which the latter are by all odds the more important. The former are either involvements of the vessel walls by frankly infectious processes, or less easily proved to be bacterial in origin, as is the case with periarteritis nodosa. Acute arteritis and phlebitis are constantly encountered and present nothing unusual. General nodal periarteritis has been seen in the lower animals, Lupke having reported before the German Pathological Society a big outbreak in cows, but it is less common than among men; we have not discovered it here.

THROMBOSES.

Thrombosis is practically always a parasitic or an infectious process although at times considerable difficulty is encountered in explaining the source of the worms or bacteria. Thus, for example, the iliac or femoral thromboses which are at the bottom of intermittent claudication, are frequently quite vague in origin. We have had one such case in a deer in which a partly occluding thrombangeitis existed in both femoral arteries and veins. Mesenteric thrombosis, a serious condition in cattle and horses from infestation with sclerostomum or strongylus, has not been proven at the Garden, but we have seen one case of numerous thromboses of the venous radicals in the jejunal wall apparently due to some nematode larvæ; the specimens were so soft by decomposition that determination was not attempted. There occurred a thrombosis of the cava and aorta originating from a necrotizing cloacitis, apparently streptococcal in nature, in a Demoiselle crane. The clot, while not totally occlusive, extended nearly as far as the heart in the vein and the abdominal aorta. There is also on record a thrombosis of the vena cava and right pulmonary vein in an American beaver, harboring Hepaticola hepatica in the liver, with a fibrosing pneumonia due to this parasite. Another case in which parasites seemed to take a hand concerned a common raccoon with tapeworms (sp.?) in the small intestine and microscopically discoverable parasitic parts in the lungs; these organs were the seat of extensive congestion and venous thrombosis, the latter containing really enormous numbers of diplococci. The parasites probably paved the way for bacterial invasion. A frank case of septic thrombotic aortitis was noted in a Rice Grackle, the infectious focus apparently being a vegetative “tricuspid” valvulitis.

ARTERITIS.

In addition to these cases, productive inflammatory changes were discovered five times affecting vessels in or near frank inflammatory processes. The animals affected with this productive process were three birds, a rodent and an elephant. In the case of two birds and the rodent the process was associated with chronic intestinal lesions, while in the elephant it was found as an endarteritis obliterans in large vessels of the lung of chronic pulmonary tuberculosis occurring in this animal. These instances serve as examples of the truly productive inflammatory processes affecting vessels and illustrate the distribution through the animal kingdom. Pathogenetically there are no essential differences, and histologically they correspond to the forms seen in man. Had every piece of tissue been subjected to microscopy wherein such lesions might have existed, more examples might have been discovered, but these processes excite no peculiar secondary effects so that attention is not drawn to them directly. The only noteworthy difference between mammals and birds is the fragile character of the clots in the latter class. This is peculiar because the principal response of this class to an infectious irritant is coagulation necrosis, liquefying enzymes apparently being absent or small in quantity.

Fatty deposits in the aortic intima are by no means uncommon in the human subject and are encountered at all ages, even in youth at a time when progressive arteriosclerosis does not accompany them. There is a belief in many quarters that this fat may be laid down and then removed. Such deposits are exceedingly rare in wild animals; when they occur it is in small indefinite patches and not the bands or rows as found in man.

TABLE 5.

Table Showing the Incidence of Degenerative Arterial Disease, the Percentage in Animals Subjected to Autopsy and the Principal Associated Pathology.

════════════════╤═════╤══════════╤═════════╤═════════╤══════════ │Total│Percentage│ Due to │Aneurysms│Myocardial │ │ of order │parasites│ │ disease │ │ │ │ │ ────────────────┼─────┼──────────┼─────────┼─────────┼────────── Primates │ 3│ .6│ │ │ 3 Carnivora │ 16│ 3.3│ 5│ 7│ 1 Ungulata │ 13│ 3.5│ 2│ │ 1 Marsupialia │ 3│ 1.8│ │ │ Total │ 35│ 1.8│ 7│ 7│ 5 │ │ │ │ │ Passeres │ 3│ .22│ │ 2│ Picariæ │ 2│ 2.2│ │ │ Psittaci │ 13│ 1.8│ │ 1│ Striges │ 3│ 2.2│ │ │ 1 Accipitres │ 13│ 6.6│ │ 1│ 4 Galli │ 5│ 1.6│ 1│ │ 4 Steganopodes│ 5│ 25.│ │ │ Herodiones │ 1│ 1.│ │ │ Palamedes │ 1│ 20.│ │ │ 1 Anseres │ 11│ 3.4│ │ 2│ 4 Struthiones │ 7│ 22.│ │ │ Alectorides │ 2│ 5.4│ │ │ 1 Total │ 66│ 1.8│ 1│ 6│ 15 ────────────────┼─────┼──────────┼─────────┼─────────┼────────── Grand Total │ 101│ 1.8│ 8│ 13│ 20 ────────────────┴─────┴──────────┴─────────┴─────────┴──────────

════════════════╤══════════╤═══════╤═════════╤══════════ │Valvulitis│ Renal │ Chronic │ Chronic │ │disease│pulmonary│infectious │ │ │ disease │ disease ────────────────┼──────────┼───────┼─────────┼────────── Primates │ │ │ │ 1 Carnivora │ │ │ 1│ 5 Ungulata │ 1│ 2│ 3│ 2 Marsupialia │ │ │ │ Total │ 1│ 2│ 4│ 8 │ │ │ │ Passeres │ │ │ │ Picariæ │ │ │ │ Psittaci │ │ 6│ 3│ 2 Striges │ 2│ │ │ Accipitres │ 2│ 5│ 2│ 4 Galli │ │ 2│ 1│ 2 Steganopodes│ 1│ 3│ │ Herodiones │ │ │ │ Palamedes │ │ 1│ │ Anseres │ 1│ 4│ 1│ Struthiones │ │ 1│ 2│ 3 Alectorides │ │ 1│ │ Total │ 4│ 25│ 9│ 11 ────────────────┼──────────┼───────┼─────────┼────────── Grand Total │ 5│ 27│ 13│ 19 ────────────────┴──────────┴───────┴─────────┴────────── For meaning of italics see foot note Table 1.

DEGENERATIVE ARTERITIS OR ARTERIOSCLEROSIS.

Whether or not it be exact to speak of the more protracted forms of vascular disease usually called arteriosclerosis or atheroma as degenerative, such changes form the most pronounced features of the lesions, and we have made such a separation at this laboratory. Here is not the place to engage in the academic discussion of the nature of the process, but I wish to state that collectively the changes as seen in such lesions in the lower animals are more degenerative than productive, and that we have never seen true ulcerative atheroma as it not uncommonly appears at the autopsy table in any large hospital. This disease of the vascular walls has long been attributed to alcohol, gout, syphilis and other such prolonged intoxications to which we might apply the light term of “toxins of civilizations.” Too little credit, or discredit has been given to chronic intestinal disorders, overeating, and overdrinking of ordinary fluids, to entirely incorrect diets, and to chronic bacterial diseases. Even though the exact counterpart of the disease in man does not occur in lower animals, we shall see the probable association with food and with habits, in a manner discordant with former teaching of the causation of the disease.

The group to which the name degenerative arteritis has been applied is, as has already been indicated, more productive than the analogues seen in the human being, but indeed it is questionable whether the lesions even in the lower animals are not more degenerative than productive. Since, however, chronic arteritis is always associated with damage to the elastic and muscular fibres of the media as well as with fatty change and overgrowth of the intima, all the deforming and degenerative cases will be classed together.

The general picture in mammals is one of diffuse rather than of plaque- like thickening, but well outlined raised or depressed areas are encountered. In the aorta and larger branches one may find irregular streaking and loss of elasticity with fairly clear, pale yellow or gray, flat sections of distinct opacity. Rarely these may contain calcareous matter, a change most often seen in the carnivores. The lesions are very largely limited to the aorta; 26 or 76 per cent. of the 35 cases had this distribution alone. The arch seemed never to be affected alone, and indeed it is rather commoner to find opaque patches stretching along the thoracic or even abdominal portion; this is especially true of the Ungulata.

FIG. 2.—ARTERIOSCLEROSIS AND ATHEROMA. THORACIC AORTA. JACKAL (CANIS AUREUS). THIS WAS CONTINUED TO THE MESENTERIC AND ILIAC VESSELS. ]

There have been also in mammals five cases of mesial change which have given rise to the picture described by Mönckeberg and usually entitled by his name. However, the noteworthy differences between the wild animal and the human cases are the absence of advanced calcification in the media under the concavities and the prominence of the changes in the aorta near the heart to be found in the former. These few cases do not permit an association of the arterial disease with any particular pathology in other parts.

Considered minutely, the outstanding lesion in the class Mammalia is the separation of the elastic fibres by fluid and debris, apparently derived from the degenerated muscle fibres, associated with a decrease of round and elliptical nuclei. Globules and hyaline pink staining material are often collected between split-up elastic strands, which fibres in some cases seem quite numerous, in others reduced. In the intima heaping-up of cells and fibres is very moderate in degree while usually one finds only subendothelial edema. When the process has advanced far, the microscopy is like that of well developed human lesions. Arterial degeneration due to parasites gives a different picture in that medial degeneration is far advanced and some fibrinocellular activity is seen upon the intima when this tissue remains. When, however, the infestation has proceeded to weaken the wall sufficient for it to give way into an aneurysm, little or no vestige of the true arterial wall is left.

In the Aves the distribution and anatomy of this process present some differences. The aorta is as usual most conspicuously the seat of change, but it is noteworthy that the dilatation or ampulla immediately above the aortic valves and from which the main vessels spring, is practically always free of lesions which are on the other hand most marked in the thoracic and abdominal sections. One’s attention is usually attracted to the aortic surface by its roughness although visibly there may be no plaques, but upon close inspection a mottled opacity may be detected. This all seems due in the few cases subjected to tissue section, to hyperplasia of endothelia, with or without fibre increase. The media may show muscular granularity or no change at all. At the stage when plaques are formed, fairly well outlined, firm but rather brittle, raised areas are detected, seated upon a distinctly opaque gray wall. The remainder of the vessel may be smooth and elastic but sometimes, in the Accipitres for instance, a general resistance to pressure and tension is found. Microscopically such a vessel will show a media the seat of ruptured muscle fibres, split-up or broken elastica and some debris, while the intima is covered with active and distinct fibrocellular exudate.

I have for comparison divided the cases into those in which the superficial productive character was prominent and those seemingly entirely a degeneration of the media, that is with inactive intima. In mammals 77 per cent. of the cases were of the degenerative type while in birds 50 per cent. were of this kind. The exact importance of this difference is not easy to evaluate, but with the facts that the bird has a greater elastic supply for its large vessels and a greater wall to calibre ratio, it is interesting. The aorta alone was affected in half of the birds, the remainder showing lesions in the carotids and femorals.

The tendency for the media to degenerate would lay the basis for concavities on the intimal surfaces after the type seen in Mönckeberg’s sclerosis. A number of cases of this variety have been encountered, but instead of being better developed in the vessels of extremities as in man they have presented more definite pictures in the aorta and pulmonary vessels. Examples will be quoted under the discussion of the various orders.

FIG. 3.—ARTERIOSCLEROSIS, ATHEROMA AND ANEURYSMAL DILATATIONS IN THORACIC AORTA. WILD CAT (FELIS RUFFUS). ]

Primates are not often affected with degenerative arterial disease, two of the instances observed showing this change confined to the coronary vessels. As might be expected the myocardium in both was affected, and in one animal had a definite concentric hypertrophy. A very interesting case was encountered in a Lion-tailed Macaque (Macacus silensis). His heart showed distinct fibrosis of the conducting pathways from auricle to ventricle and of the papillary muscles. No atheroma was present in the aorta, but in the pulmonary distinct sacculations of the Mönckeberg type were found. Mesial degeneration was apparently responsible, but no calcification had occurred. Death was due to acute gastritis.

Carnivora present about half the cases seen in mammals and 16 per cent. of the total. Five of the sixteen cases owe their origin to parasitic arteritis and were combined with aneurysms. As will be noted by consultation of the list there is no outstanding accompanying pathology, a fact which makes parasites more important. One case of mesial degeneration, resembling the Mönckeberg type was observed in the thoracic aorta of a bear.

Ungulata are generously represented, thirteen cases being recorded distributed rather unevenly between the odd-toed (1 or 8.5 per cent.) and even-toed groups (12 or 2.9 per cent.). The single case in the first group occurred in a Zebra (Equus burchelli) wherein was found about the middle of the thoracic aorta a diffuse thickening of media and intima in a circular plaque approximately two centimetres in diameter; it was by no means so well developed as similar lesions in the even-toed ungulates. This recalls the expression of doubt by Zinserling as to the occurrence in the horse of arteriosclerosis similar to that in human beings.

The lesions in the Artiodactyla are both in plaques and diffuse, the aorta and its branches sometimes being quite wrinkled but beset with firm elevations with and without calcification. These changes are fairly definite and, although they never attain the development seen in man, resemble the stage of wrinkling and roughness in the preulcerative stage of the human analogue. Two of the cases were associated with dilatations of the mesenteric vessels and with periarteritis, a picture strongly suggesting parasitic infestation; in one case ineffectual search was made, in the other no record is made of the parasites. Renal disease occurred only twice and myocardial damage only once. Chronic pulmonary disease, present thrice, took the form of tuberculosis twice and pleural adhesions with atelectasis once.

Marsupialia present three quite interesting cases, a Tasmanian Devil (Sarcophilus ursinus) and two Kangaroos (Macropus). The first showed distinct sacculations in the ascending aorta, suggestive of Mönckeberg’s sclerosis but equally resembling several small or incomplete aneurysms. The underlying vessel was opaque and stiff, continuing so to the middle of the thoracic portion. The other marsupials showed distinct mesial damage with early calcification and a roughened intima; once the pulmonary artery was involved.

It will be noticed that the orders Rodentia and Lemures are missing from those showing arterial disease although we have a reasonable number of autopsies upon them.

Passeres are hardly good exponents of vascular disease, an interesting thing in view of their large heart, heavy vessels, and flying habits. It is, however, striking that two of the three birds of this group had aneurysms of the aorta, one of which ruptured just above the origin, partly into and partly outside the pericardium. Despite several microscopical sections we were unable to find the tiny ends of the breach and any evidence of parasites. In the other case a vegetative growth occurred on the intima near the dilatation.

FIG. 4.—ARTERIOSCLEROSIS IN AORTA. OTTER (LUTRA CANADENSIS). THERE IS RELATIVELY LITTLE INTIMAL CHANGE, THE MEDIA BEING FIBROTIC AND ALLOWING THE INTIMA TO BE DEPRESSED IN SMALL CONCAVITIES. ]

The Picariæ were represented by a Hornbill and a Toucan. The former presented roughened yellowish elevations for two centimetres above the aortic valve; this seemed the only involvement. The Toucan had a few small scattered but deep yellow plaques in the same location.

Psittaci, although failing to be accredited with a high percentage of arterial disease, nevertheless present some striking and interesting changes. In the first place, the central vessels are not so conspicuously the principal seat of atheroma as is the case in many other orders, and the lesions are not so productive. It is usual to find flat areas of opacity, perceptible as easily by section through the wall as by holding up the opened vessel to the light, the seat of the density being in the media. This can be followed into the wing arteries and, upon microscopic section, these smaller vessels will show mesial degeneration, thus being comparable to arteriocapillary fibrosis of man. However frequent this picture may be, there are also instances of overgrowth in the intima, prominences over opacities or raised plaques at the points of branching, lesions which correspond to the activity of the inner coat. It is interesting that renal disease, chronic pulmonary and general infections occur in a goodly proportion of these birds.

Striges is an order of little importance. The lesions in the two cases consisted of rather prominent plaques in aorta and large branches.

Accipitres stand out as giving the greatest percentage of any order of which we have had a fair number upon which to make comparisons. Their arterial lesions are frequently accompanied by renal, myocardial and valvular disease. Mesial and intimal alterations are about equal in degree, irregular patches going on to softening without ulceration, and early calcification being quite prominent. The sickle at the branching of the renals is a favorite site of deposit. Like the parrots their arterial damage is not confined to the aorta, but may be found in the carotids, femorals or small wing arteries. The most common situation is, however, in the lower thoracic and renal regions.

Galli, represented by five specimens, seem to have their vascular disease accompanied very often by myocardial and infectious disease. Their arterial pathology consists of raised gray patches in the aorta only.

Steganopodes give the highest percentage among avian orders, but this must be held sub judice because of the small number of specimens subjected to autopsy. Renal disease occurred in three cases. Their lesions are in the form of yellow opaque streakings in the aorta and its branches, in one case following the carotid half way up the neck. Plaques are not common, and when they occur are streaky and illy outlined.

Herodiones, represented only by a heron, are negligible. This bird showed a diffuse thickening with early thrombotic deposits attached to the intima.

Palamedes are represented by a Screamer which showed around the orifices of the renal arteries an early fatty deposit and mesial opacity.

Anseres present a considerable number of cases which are accompanied by cardiac, renal and general pathology. The character of the lesions is like that of the Accipitres and the distribution differs in only one particular. In four of these eleven cases the elevations or opaque areas were limited entirely to the stretch of aorta which might be compared to the arch in mammalia, that is the part with which the right subclavian is in closest contact and which bends almost directly backward to become the thoracic aorta. This excludes the ampulla just above the aortic valves. There seems no real reason for this and it may be accidental.

FIG. 5.—AORTIC ARTERIOSCLEROSIS. SARUS CRANE (GRUS ANTIGONE). THE LESIONS ARE ELEVATED AND IRREGULAR. ]

Struthiones, with seven specimens having arterial disease in the great vessels alone, seem to have no especial characters unless these be in the heavy furrowing and stiffness of the wall, with opaque, elevated, indefinite patches, seen mostly in the descending aorta; once a long tough and partly brittle stretch was found in the carotid.

Alectorides, with a relatively high percentage, present irregularly outlined fatty and finely granular patches in the intima of the lower aorta and abdominal vessels, and, in two cases, as far as the vessels of the lower extremities could be followed.

The orders Columbæ and Fulicariæ are missing from the list of Aves having arterial disease, yet a reasonable number of autopsy records are at hand.

SUMMARY ON ARTERIOSCLEROSIS.

Having discussed the orders separately, a review of the whole situation is desirable. Chronic arteritis, or as it is usually called arteriosclerosis, is common to very many zoological orders, and its principal lesions are comparable throughout the two classes under consideration. A statement as to its incidence would best be made by adopting an arbitrary number of observations as the desired minimum upon which to draw conclusions, and I shall adopt one hundred as such a figure. Accepting this as reasonable, a review of the table indicates that the order of percentage incidence is: Accipitres 6.6, Ungulata 3.5, Anseres 3.4, Carnivora 3.3, Striges 2.2, Psittaci 1.8, Marsupialia 1.8, Galli 1.6, Primates 0.6, Passeres 0.22; the other orders have less than one hundred specimens each. There is no doubt that carnivorous birds have the highest incidence of chronic arterial disease. Next in order come three varieties with nearly equal incidence, the ungulates, anserine birds and carnivorous mammals. These orders have little in common unless it be that in nature they are often engaged in prolonged or strenuous effort, as in fight or flight. We possess no measurement of their vascular supply but by consultation of the table giving heart weights (page 63) it will be found that three of them have values below that of the class in which they belong; the Carnivora alone have a greater heart-to-body ratio than the average for its class Mammalia. Nor do these orders have any direct dietetic relationship. The expected longevity of these groups does not permit one to discover any reason for arterial changes except perhaps that they have a reasonably good viability under park conditions, and therefore many have a longer opportunity to develop vascular disease. It so happens, however, that the first four groups are the most likely to suffer from gastrointestinal inflammation, of dietetic or bacterial origin.

It is interesting, but not easily explicable that the orders of great activity, Primates and Passeres, are at the end of the list; their food is very largely carbohydrate in character. Just why Lemures, Rodentia and Columbæ should be missing is not quite clear, because orders of comparative habits and food are included.

A review of the concomitant pathology reveals the fact that nephritis more often accompanies these processes than any other single condition. Among the chronic infectious disease in the table is included chronic enteritis; this group falls well behind the renal diseases. The relatively small number of cases of valvulitis speaks rather against an active infectious origin of the vascular lesions.

ANEURYSMS.

Aneurysms have been observed all over the world and in nearly all the larger orders. The London Garden has had an unusually large number to report, the most striking being that described by Seligman in the 1906 Report of the Society, in a tiger thirteen years in captivity which had fourteen sacculations from pea to plum size scattered along the aorta. Even with the number of cases on record and those collected here it would be unwise to draw deductions as to their incidence or as to the possibilities of vascular dilatation in any given order. Horses have aneurysms occasionally, cows and dogs rarely, according to Rievel. I can, however, state that there has not occurred in our experience a large growing pulsating aneurysm in the aortic arch region comparable to the condition so well known in man. The literature to which we have had access gives a definite impression that parasitism of vessel walls is the most important factor in the causation of ectasia, and that simple non-parasitic arteriosclerosis is relatively unimportant. Two of our seven cases seem to have been free of parasites but the notes cannot entirely assure one of this. The distribution of cases at this Garden is found in Table 5.

FIG. 6.—PARASITIC ANEURYSM IN THORACIC AORTA. PARADOXURE (PARADOXURUS LEUCOMYSTAX). PARTLY SACCULAR, PARTLY DISSECTING ANEURYSM WITH OPEN THROMBOSIS AS INDICATED BY THE GLASS ROD. PIECES OF WORM FOUND IN WALL. COULD NOT OBTAIN WHOLE SPECIMEN, SPECIES UNDETERMINED. ]

A dilatation of the first part of the arch in a seal to a size which might be described as an aneurysm caused us to make such a diagnosis, correctly enough from the size and shape of the vessel but possibly worthy of reconsideration in light of the fact that no damage to the wall was found. At the heart and in the descending arch the diameter measured 4–5 cm., while the first part of the aorta measured 7.5 cm. This great irregularity in width could not be found in other seals albeit this section of the arch is usually a trifle larger than its origin and descending portion. The cava in seals is also large, but in this particular animal it measured 6 cm. across at the liver where there is a normal dilatation. These two spaces are looked upon as normal reservoirs for blood during diving, but the case in question seemed to have excessive “aneurysmoid” enlargements without mural disease. London reports an aneurysm of the aorta in a seal.

Aneurysms are not so common in birds, the incidence being in comparison with mammals as 1 to 2.2. Two seats are prominent for their development: the sinuses above the aortic valves and the first part of the subclavian vessels; two of the six cases occupied the first position, two the second, while one other lay in the arch of the aorta, the last in its descending thoracic portion. Those developing over the valves seem to arise from simple degenerative arteritis; those that occupy the other locations are apt to be surrounded by plaques on the intima. Aneurysms in birds reveal by microscopy some trace of all the vascular coats and seem not to construct an adventitia from surrounding areolar tissue. The veins have presented no peculiar pathology, except in tumors which will be taken up later. A Derby’s Tyran showed a phlebitis and periphlebitis of the left subclavian vein, of mycotic nature, which led to death by rupture and hemorrhage.