Part 38

The =thorax= is distinctly barrel-like and is not decidedly compressed anteriorly like that of the horse and ox. The inlet is oval and is relatively wide on account of the marked curvature of the first pair of ribs and cartilages.

BONES OF THE SKULL

In the following descriptions of the separate bones an intermediate type—e. g., a fox terrier—is selected, and the most striking differences in the brachycephalic and dolichocephalic breeds will be considered in the section on the skull as a whole.

CRANIUM

FIG. 122.—BASE OF SKULL OF DOG, WITHOUT MANDIBLE.

I, Occipital; II, tympanic part of temporal; IIa, squamous part of temporal; IIb, mastoid part of temporal; III, sphenoid; IV, pterygoid; V, palate bone; VI, vomer; VII, malar; VIII, zygomatic arch; IX, inner wall of orbit; X, palatine process of maxilla; XI, premaxilla; XII, orbital cavity; 1, 1, tubercles above foramen magnum; 2, foramen magnum; 3, occipital condyle; 4, notch between occipital condyles; 5, condyloid fossa; 6, hypoglossal foramen; 7, paramastoid (styloid, jugular) process; 8, for. lacerum and posterior opening of carotid canal; 9, petro-occipital synchondrosis; 10, petro-tympanic fissure; 11, tubercle; 12, bulla ossea; 13, muscular process of petrous; 14, carotid foramen; 15, osseous Eustachian tube; 16, postglenoid process; 17, glenoid cavity; 18, for. ovale; 19, posterior opening of alar canal; 20, external opening of parieto-temporal canal; 21, stylo-mastoid foramen; 22, external auditory meatus; 23, temporal crest; 24, zygomatic process of temporal bone; 25, body of postsphenoid; 26, body of presphenoid; 27, anterior opening of alar canal; 28, for. lacerum orbitale; 29, optic foramen; 30, hamulus of pterygoid; 31, horizontal part of palate bone; 32, perpendicular part of palate bone; 33, median palatine suture; 34, palato-maxillary suture; 35, posterior nasal spine; 36, anterior palatine foramen; 37, palatine groove; 38, alveolar border of maxilla; 39, palatine process of maxilla; 40, pterygoid process of maxilla; 41, palatine fissure; 42, body of premaxilla; 43, palatine process of premaxilla; 44, alveolar border of premaxilla; 45, supraorbital process of frontal bone. (Ellenberger-Baum, Anat. d. Hundes.) ]

The =occipital bone= is similar in position to that of the horse. The crest, is prominent, angular, and directed backward. Just below the crest are two rough imprints or tubercles for muscular attachment. The surface below these is convex from side to side and concave from above downward. On either side, at the junction with the squamous, there is a foramen which communicates with the parieto-temporal canal. The condyles are somewhat flattened and are widely separated above; at the inner side of each is a short condyloid canal, which opens into the parieto-temporal canal. The paramastoid processes are very short. The basilar part is wide and joins the bulla ossea on either side; its lower surface is flattened and the tubercles are at the junction with the bulla. The hypoglossal foramen is small and is close to the foramen lacerum posterius; the latter is bounded in front by the bulla ossea, behind and internally by the occipital bone.

The =interparietal bone= fuses with the occipital before birth. It forms the high posterior part of the sagittal crest, and is wedged in between the two parietal bones. The tentorium osseum is thin and curved, concave ventrally. Its base concurs with the occipital and parietal bones in the formation of a transverse canal which is continuous with the parieto-temporal canals.

FIG. 123.—SKULL OF DOG, DORSAL VIEW.

I, Occipital; II, parietal; III, frontal; IV, lacrimal; V, malar; VI, squamous temporal; VII, nasal; VIII, maxilla; IX, premaxilla; 1, supraoccipital; 2, interparietal; 3, parieto-occipital suture; 4, occipital crest; 5, sagittal crest; 6, parieto-frontal suture; 7, squamous suture; 8, parietal eminence; 9, antero-external angle of parietal bone; 10, frontal crest; 11, 14, orbital margin; 12, supraorbital process; 13, frontal fossa; 15, temporal part of frontal bone; 16, nasal process of frontal bone; 17, frontal suture; 18, lacrimal foramen; 19, maxillary process of frontal bone; 20, lacrimo-maxillary suture; 21, frontal process of malar bone; 22, lacrimal process of malar; 23, zygomatic process of malar; 24, zygomatic process of squamous temporal; 24′, posterior end of nasal bone; 25, nasal suture; 26, anterior end of nasal bone; 27, infraorbital foramen; 28, canine tooth; 29, cheek tooth; 30, frontal process of maxilla; 31, body, 32, nasal process, 33, palatine process of premaxilla; 34, palatine fissure; 35, incisor teeth. (Ellenberger-Baum, Anat. d. Hundes.) ]

The =parietal bone= is rhomboid in outline and is strongly curved. It is extensive and forms the greater part of the roof of the cranial cavity. At the junction of the right and left bones there is a prominent sagittal crest which is continued upon the frontal bones. The lower border articulates with the temporal wing of the sphenoid by its anterior part and with the squamous temporal in the remainder of its extent. The external surface enters into the formation of the temporal fossa. The internal surface is marked by digital impressions, and by grooves for the middle meningeal artery and its branches.

The external surface of the =frontal bone= is crossed by a frontal crest, which extends in a curve from the sagittal crest to the supraorbital process, and separates the frontal and temporal parts. The frontal parts of the two bones form a central depression and slope downward and forward. The supraorbital process is very short, so that the orbital margin is incomplete as in the pig. The supraorbital foramen is absent. In front there is a narrow pointed nasal part which fits in between the nasal bone and the maxilla. The orbital and temporal parts are relatively extensive. Two ethmoidal foramina are commonly present. The frontal sinus is confined to the frontal bone.

The parts of the =temporal bone= fuse early. The zygomatic process curves widely outward and forward. Its anterior part is beveled below and articulates extensively with the corresponding process of the malar. The articular surface for the condyle of the mandible consists of a transverse groove which is continued upon the front of the large postglenoid process. Behind the latter is the lower opening of the parieto-temporal canal. There is no condyle. The mastoid part is small, but bears a distinct mastoid process. The external auditory meatus is large and the canal very short, so that one can see into the tympanum in the dry skull. The India ossea is very large and is rounded and smooth; the inner side is united to the basioccipital. Above this junction and roofed in by the union of the petrous part and the basioccipital is the =petro-basilar canal= (Canalis petrobasilaris); this transmits a vein from the floor of the cranium to the foramen lacerum posterius. The latter is in reality a depression and is situated behind the bulla ossea. In its posterior part is a foramen which transmits the ninth, tenth, and eleventh cranial nerves. The =carotid canal= branches off from the petro-basilar, passes forward external to it through the inner part of the bulla ossea, and opens in front at the =carotid foramen=; it transmits the internal carotid artery. The Eustachian opening is immediately external to the carotid foramen. The muscular and hyoid processes are extremely rudimentary. The petrous part projects into the cranial cavity and forms a sharp prominent petrosal crest. The inner surface presents a deep =floccular fossa= above the internal auditory meatus. The anterior surface is also free. The anterior angle is perforated by a =canal= for the fifth cranial nerve (Canalis nervi trigemini).

FIG. 124.—CRANIAL CAVITY OF DOG, AS SEEN ON SAGITTAL SECTION OF SKULL.

I, Roof of cranium; II, base of cranium; III, posterior wall of cranium; IV, anterior wall of cranium; A, anterior cranial fossa; B, middle cranial fossa; C, posterior cranial fossa; a, body of presphenoid; a′, body of postsphenoid; c, palate bone; d, vomer; e, occipital; f, occipital condyle; g, sagittal crest; h, frontal sinus; h′, cranial plate of frontal bone; i, cribriform plate of ethmoid bone; i′, ethmoidal foramen; k, ethmoturbinals; l, parietal bone; l′, l″, squamous temporal bone; l‴, temporal wing of sphenoid bone; m, sella turcica; m′, dorsum sellæ; n, optic foramen; o, foramen lacerum orbitale; p, foramen rotundum; q, foramen ovale; r, r′, carotid foramina; s, tentorium osseum; t, foramen lacerum; u, u′, orifices of parieto-temporal canal; v, condyloid canal; w, canal for trigeminal nerve; x, internal auditory meatus; y, y′, orifices of canal for inferior occipital sinus; z, floccular fossa. (After Ellenberger, in Leisering’s Atlas.) ]

The body of the =sphenoid bone= is flattened dorso-ventrally. The sella turcica is shallow, but the dorsum sellæ is well developed and bears =posterior clinoid processes=. A pair of =anterior clinoid processes= project back from the roots of the orbital wings. The latter are relatively small and are crossed externally by a crest, which is continued forward upon the palate bone. The temporal wings are extensive and articulate above with the parietals. Perforating the roots of the wings are the following foramina, named from before backward: The optic passes through the orbital wing. The foramen lacerum orbitale is a little lower and is at the junction of the wings. The foramen rotundum opens into the alar canal, which passes through the root of the short but wide pterygoid process. The foramen ovale is near the posterior border of the temporal wing. There is no sphenoidal sinus.

The =ethmoid bone= is highly developed. The cribriform plate is extensive, and the olfactory fossæ are very deep. The crista galli is little developed, and often incomplete. The perpendicular plate is long. The lateral masses are greatly developed and bulge upward into the frontal sinus. There are four large endoturbinals and six ectoturbinals. The lamina papyracea is extensive and forms the inner wall of the maxillary sinus. Its lower border joins the palatine process of the maxilla and the horizontal part of the palate bone. A shelf-like plate extends inward from its lower part and concurs with the similarly incurved part of the palate bone in forming the =transverse lamina= (Lamina transversalis), which divides the olfactory fundus of the nasal cavity from the naso-pharyngeal meatus.

FACE

The =maxilla= is short, but very high posteriorly. The facial crest is absent. The infraorbital foramen is over the alveolus for the third premolar. The =frontal process= fits into a deep notch between the nasal and orbital parts of the frontal bone, and the middle part of the posterior border lies along the orbital margin. There are more or less pronounced ridges, juga alveolaria, over the canine and molar teeth. The zygomatic process is short and thin; it is completely overlapped outwardly by the malar, and is perforated by a number of foramina (Foramina alveolaria). A maxillary tuberosity is not present in the adult, but there is a pointed projection, the pterygoid process, behind the last alveolus. The internal surface bears a short turbinal crest on its anterior part, behind which it is deeply concave and forms the outer wall of the maxillary sinus. The palatine process is short, wide behind, and moderately arched from side to side. The anterior palatine foramen is situated at or close to the transverse palatine suture about midway between the median suture and the alveolar border. The palatine groove is distinct. The large alveolus for the canine tooth is completed by the premaxilla. The small alveolus for the first premolar is separated from the preceding one by a small interval. The next two consist of anterior and posterior parts for the roots of the teeth. The fourth and fifth are much larger and are divided into three parts. The last is small and consists of three divisions. The infraorbital canal is short.

The body of the =premaxilla= is compressed dorso-ventrally, and contains three alveoli for the incisor teeth, which increase in size from first to third; it also completes the inner wall of the large alveolus for the canine tooth. The foramen incisivum is very small except in large skulls. The interalveolar border is wide and very short. The nasal process is wide at its origin and tapers to a sharp point behind; the anterior part curves upward, backward, and a little inward, and forms the lateral margin of the osseous nasal aperture; the posterior part extends backward a long distance between the nasal bone and the maxilla. The palatine process turns upward and outward, forming with its fellow a wide groove for the septal cartilage; the posterior end is pointed and fits into a notch between the palatine processes of the maxillæ, and supports the end of the vomer. The palatine fissure is short but wide.

The horizontal part of the =palate bones= is extensive, forming about one-third of the hard palate. It presents a variable number of lesser palatine foramina. There is usually a pointed posterior nasal spine at the end of the median suture. The palatine canal is sometimes formed entirely in this bone. The perpendicular part is even more extensive. Its external surface is chiefly free and forms most of the inner wall of the large pterygo-palatine fossa. The maxillary foramen is situated in a deep recess between this bone and the zygomatic process of the maxilla. Just above it there is commonly another foramen which opens into the nasal cavity. The posterior palatine and sphenopalatine foramina are situated further back and a little lower; the former is immediately below the latter. A horizontal plate extends from the inner surface, meets that of the opposite bone and completes the lamina transversalis spoken of in the description of the ethmoid bone. There is no palatine sinus.

The =pterygoid bones= are very wide and short. They form a considerable part of the lateral boundaries of the posterior nares. The lower and posterior holders are free and at their angle of junction there is a variable hamulus.

The =nasal bones= are (in most breeds) long and wider in front than behind. The external surface is variably concave in its length and is inclined toward the median suture so as to form a central groove. The inner borders turn downward and form an internal nasal crest which becomes very prominent behind. The posterior parts fit into a notch formed by the frontal bones. The anterior ends form an almost semicircular nasal notch.

The =lacrimal bone= is very small. The facial part extends very little or not at all beyond the orbital margin. The orbital surface is small and triangular, and presents the entrance to the lacrimal canal.

FIG. 125.—MANDIBLE OF DOG, RIGHT-ANTERIOR VIEW.

a, Right ramus; b, left ramus; c, body; d, alveolar border; e, processus angularis; f, condyle; g, coronoid process; h, masseteric fossa; i, k, crests which form the upper and lower boundaries of fossa; l, mandibular foramen; m, mental foramina; n, masseteric line; o, sigmoid notch. (Ellenberger-Baum, Anat. d. Hundes.) ]

The large zygomatic process constitutes the bulk of the =malar bone=. It is very long and is strongly curved. The upper border is convex, free in front, where it forms part of the orbital margin, beveled behind for articulation with the similar process of the temporal bone. Between these it bears an eminence, the processus frontalis, to which the orbital ligament is attached. The body of the bone may be considered to consist of a =lacrimal process= directed upward and fitting in between the lacrimal and maxilla, and a =maxillary process= directed downward. The facial surface is convex.

The =superior turbinal bone= is in its anterior part a simple plate, attached by one edge to the nasal bone; it curves downward and inward, and its free border is thickened and everted. The posterior part is wider and resembles the ethmoturbinals, with which it is connected.