Part 179

The =inferior longitudinal= or =sagittal sinus= (S. sagittalis inferior) runs backward on the upper surface of the corpus callosum along the concave edge of the falx cerebri and joins the great cerebral vein (of Galen) to form the straight sinus.

The =straight sinus= (S. rectus) passes upward and backward between the cerebral hemispheres and in the tentorium cerebelli and joins the superior sagittal sinus. The point of meeting is the confluence of the sinuses (Confluens sinuum).

The =occipital sinuses= (S. occipitales) lie on either side of the vermis cerebelli. They empty anteriorly into the sinus communicans and communicate behind with the spinal veins.

The =superior petrosal sinuses= (S. petrosi superiores) pass in the tentorium cerebelli to end in the transverse sinuses.

The =basilar system= consists of the following:

The =cavernous sinuses= (S. cavernosi) lie in the inner grooves of the root of the temporal wings of the sphenoid bone at either side of the sella turcica. The two are connected by a wide traverse branch (Sinus intercavernosus) behind and below the posterior part of the pituitary body. Each is continuous in front with the ophthalmic vein and below with the inferior petrosal sinus. The third, sixth, and the ophthalmic and maxillary divisions of the fifth nerve lie along the outer wall of the sinus. The internal carotid artery traverses the sinus and is connected with its fellow by a transverse branch which lies in the corresponding part of the sinus. An oval opening in the floor communicates with the inferior petrosal sinus and transmits the internal carotid artery.

The sinus is not subdivided by strands of fibrous tissue as in man, but a few delicate bands attach the artery to its wall.

The =inferior petrosal sinuses= (S. petrosi inferiores) lie along the borders of the basilar part of the occipital bone, inclosed in the thick dura which closes the foramen lacerum. The anterior part extends about half an inch (ca. 12 mm.) under the temporal wing of the sphenoid. Here communications exist with veins in the pterygo-palatine fossa. The posterior end is bulbous and lies in the condyloid fossa; it communicates with the condyloid vein issuing from the hypoglossal foramen and is drained by the inferior cerebral vein; it also receives an emissary vein from the parieto-temporal canal. The roof of the sinus is perforated by an oval opening at the carotid notch which opens into the cavernous sinus and transmits the internal carotid artery; the latter forms the first bend of its =S=-shaped curve in the petrosal and the second in the cavernous sinus.

The =basilar plexus= (Plexus basilaris) is a venous plexus situated on the upper surface of the basilar part of the occipital bone. It is connected through the hypoglossal foramen with the inferior petrosal sinus and communicates behind with the spinal veins.

THE VEINS OF THE CRANIUM

The =veins of the brain= (Venæ cerebri) do not in general accompany the cerebral arteries. They have very thin walls, no muscular coat, and no valves. They are arranged in two sets, superficial or cortical and deep or central. The superficial veins are more numerous and larger than the arteries. They lie on the surface of the brain in the pia mater and the subarachnoid space.

The =superior cerebral veins= drain the upper and outer part of the cerebral cortex. They receive veins from the medial surfaces of the hemispheres and open into the superior sagittal sinus. Their terminal parts are bulbous and their openings are directed obliquely forward, i. e., contrary to the direction of the bloodstream in the sinus.

The =inferior cerebral veins= lie on the inferior and external aspect of the hemispheres. They open into the inferior system of sinuses. The =middle cerebral vein= runs in the lateral fissure (of Sylvius) and opens into the cavernous sinus.

The =deep cerebral veins= issue from the central or ganglionic parts of the brain at the transverse fissure. They converge to form the =great cerebral vein= (of Galen) (V. magna cerebri). This passes upward and backward behind the splenium of the corpus callosum and is continued as the straight sinus to join the sagittal sinus.

The =superior cerebellar veins= ramify on the upper surface of the cerebellum. They open into the superior system of sinuses and the great cerebral vein. The =inferior cerebellar veins= are larger and go chiefly to the basilar plexus. The veins of the medulla and pons end in the inferior system of sinuses.

The =meningeal veins= (Venæ meningeæ) arise in capillary plexuses in the superficial and deep faces of the dura mater. Some end in the sinuses of the dura, others accompany the meningeal arteries.

The =diploic veins= (Venæ diploicæ) are anastomosing channels in the spongy substance of the cranial bones. Their walls are thin, consisting in many places only of the endothelium, and they have no valves. Some open inward into venous sinuses, others into extracranial veins.

SPINAL VEINS

Two =longitudinal spinal veins= or =sinuses= (Sinus columnæ vertebralis) extend along the floor of the vertebral canal, one on either side of the superior common ligament. They are continuous in front with the basilar plexus. They lie in the grooves on the bodies of the vertebræ and are connected by a series of transverse anastomoses which pass between the central part of the bodies of the vertebræ and the superior common ligament or in channels in the bone. They receive veins from the spinal cord, the dura mater, and the bodies of the vertebræ (Venæ basis vertebræ). Through the intervertebral foramina efferent vessels connect with the vertebral, intercostal, lumbar, and lateral sacral veins.

VEINS OF THE THORACIC LIMB

The =brachial vein= (V. brachialis) is a satellite of the extrathoracic part of the brachial artery. It arises at the inner side of the distal end of the shaft of the humerus and passes upward in the arm behind the artery under cover of a layer of fascia and the posterior superficial pectoral muscle. At the shoulder it is ventral to the artery, crosses the anterior border of the first rib, and concurs with its fellow and the two jugulars in the formation of the anterior vena cava. The roots of the vein are somewhat variable, but most often four radial veins in addition to a large oblique branch from the cephalic unite in its formation. Its tributaries correspond in general to the branches of the artery, but a few differences are worthy of notice. The =thoracico-dorsal vein= joins the brachial directly or opens into the deep brachial. The =external thoracic= or =“spur” vein= (V. thoracica externa) is a large vessel which arises in the ventral wall of the abdomen, passes forward (embedded more or less in the panniculus) along the outer border of the posterior deep pectoral muscle, and joins the brachial vein near the first rib. It often communicates with the subscapular vein.

FIG. 465.—SPINAL VESSELS OF HORSE.

The vertebral canal has been opened by sawing off the arches. The nerve-roots are cut on one side and the spinal cord turned over to right. 1, Ventral or middle spinal artery; 2, reinforcing branches from vertebral, intercostal, or lumbar arteries (according to region); 3, longitudinal vertebral sinuses; a, ventral surface of spinal cord; b, dura mater (cut); c, nerve-roots; d, superior common ligament. (After Ellenberger, in Leisering’s Atlas.) ]

The =cephalic vein= (V. cephalica) arises at the inner side of the carpus as the continuation of the internal superficial metacarpal vein. It runs upward on the deep fascia of the forearm at first in the furrow between the flexor carpi internus and the radius. Toward the middle of the forearm it inclines gradually forward on the inner surface of the radius, accompanied by a cutaneous branch of the median nerve, and arrives at the insertion of the biceps. Here it detaches a large branch (Ramus communicans) which passes upward and backward over the inner insertion of the biceps, the posterior radial artery, and the median nerve, and joins the brachial vein. The vein to this point is often termed the internal subcutaneous vein of the forearm (V. cephalica antebrachii). It is continued (as the V. cephalica humeri) in the furrow between the mastoido-humeralis and the anterior superficial pectoral with a branch of the inferior cervical artery, crosses the deep face of the cervical panniculus, and opens into the terminal part of the jugular or the brachial vein. It receives an =accessory cephalic vein= (V. cephalica accessoria), which arises from the carpal network, runs upward along the inner border of the extensor carpi, turns along the lower border of the brachialis, passes under the superficial tendon of the biceps and joins the cephalic.

FIG. 466.—DISSECTION OF PECTORAL REGION AND ANTERIOR PART OF ABDOMINAL WALL OF HORSE.

1, Jugular vein; 2, loose connective tissue of axillary space; 3, ascending branch of inferior cervical artery; 4, descending branch of same; 5, cephalic vein; 6, median nerve; 7, ulnar nerve; 8, brachial artery; 9, brachial vein; 10, external thoracic or “spur” vein; 11, anterior abdominal artery and vein; 12, branches of sixth cervical nerve; 13, cutaneous branch of axillary nerve; 14, cutaneous branch of musculo-cutaneous nerve; 15, cervical panniculus; 16, sterno-cephalicus; 17, scalenus; 18, mastoido-humeralis; 19, anterior superficial pectoral; 20, posterior superficial pectoral; 21, anterior deep pectoral; 22, posterior deep pectoral; 23, abdominal panniculus; 24, obliquus abdominis externus; 25, rectus abdominis; 26, coraco-brachialis; 27, tensor fasciæ antibrachii; a, prescapular lymph glands; b, prepectoral lymph glands; c, axillary lymph glands; d, cubital lymph glands; c.x., xiphoid cartilage. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

The deep veins of the forearm are variable. Commonly two =posterior radial veins= (Venæ medianoradiales) accompany the artery of like name, one in front and one behind. A third vein arises by radicles emerging from the proximal part of the deep flexor; it joins the posterior satellite of the posterior radial artery or forms one of the roots of the brachial vein. The =common interosseous vein= joins the posterior satellite. The =anterior radial vein= (V. collateralis radialis) is a satellite of the artery. The =ulnar vein= is usually double at its proximal part, and communicates with the deep brachial vein.

There are three chief =metacarpal veins=. The =internal metacarpal vein= (V. metacarpea volaris superficialis medialis) arises from the volar venous arch above the fetlock. It is the largest vein of the region and lies in front of the large metacarpal artery. It separates from the artery at the proximal end of the metacarpus, passes upward on the inner part of the posterior surface of the carpus, under cover of the superficial layer of the posterior annular ligament, and is continued as the cephalic vein. It communicates at its proximal part with the origin of the posterior radial veins by a short but relatively large branch. The =external metacarpal vein= (V. metacarpea volaris superficialis lateralis) arises from the venous arch above the fetlock and passes upward behind the external border of the suspensory ligament in front of the external branch of the median nerve and accompanied by a small artery. At the proximal end of the metacarpus it is connected with the deep metacarpal vein by two transverse anastomoses which pass across the suspensory ligament. It then passes upward as a satellite of the external volar metacarpal artery and concurs in the origin of the ulnar and posterior radial veins. The =deep metacarpal vein= (V. metacarpea volaris profunda medialis) arises from the venous arch, passes forward between the two branches of the suspensory ligament, and ascends on the posterior surface of the large metacarpal bone. At the proximal end of the latter it communicates with the other metacarpal veins, ascends with the small metacarpal artery, and concurs in forming the radial veins.