Part 65

The adventitia is composed of loose connective tissue with some elastic fibers. A few smooth muscle cells are present, which, as are also the elastic fibers, are arranged longitudinally. The adventitia, blending with the connective tissue surrounding the arteries, serves to anchor the vessels to the surrounding structure.

=Structure of the Veins.=—In many respects the walls of the veins resemble those of the arteries. The same three coats exist and the same elements enter into their structure. The transition from capillary to small veins, and from those to larger veins, is similar to the transition from the arteries to capillaries, in inverse order. The walls are not so thick as those of arteries. The elastic tissue is much less in quantity and in smaller veins disappears. There is not a clear line of demarcation between the intima and the media.

The veins of birds differ from those of mammals in that they have fewer valves. The valves are also less perfect, and often permit a backward flow of blood.

The walls of the arteries and of the veins are supplied with nutrient blood-vessels. These are called the vasa vasorum, or blood-vessels of the blood-vessel wall. They are mostly in the adventitia. They may arise from the vessel to which they are distributed or take origin from an adjacent vessel. These small arteries supplying the vessel coat after terminating into capillaries form small veins through which the blood, from the structure of the vessel wall, is returned.

The walls of the blood-vessels are supplied with both medullated and non-medullated nerves. The non-medullated nerve fibers are axones of the sympathetic neurones and control the caliber of the vessels. These fibers are called the vasomotor nerves. They form plexuses in the adventitia, from which are given off branches which penetrate the media and terminate on the muscle cells. The medullated nerves are the axones of the spinal nerves. The larger fibers are found in the connective tissue outside the adventitia and give off branches to the media where they divide repeatedly, lose their sheath, and terminate in the media and at times in the intima.

THE ARTERIAL TRUNKS

The common aorta is short; it originates from the left ventricle (Fig. 61B, No. K, 14), and is guarded by three semi-lunar valves. The aorta breaks through the pericardium just to the right of the pulmonary arteries in a ventral direction; it then turns upward dorsally and to the right of the inferior bodies of the vertebræ. It is then directed anteriorly, and dorsally to the right bronchus, between the right bronchus and the right lung. The right and the left coronaries are given off from the common aorta; they have been discussed. There is next given off the left brachio-cephalic or brachio-cephalic sinister artery (Fig. 61B, No. K, 10), which is just above the border of the base of the heart. This artery passes upward and slightly forward, over the center of the inferior larynx. Just beyond this point the subclavian artery is given off; this artery later becomes the axillary and the axillary the brachial artery. Then there is given off the anterior and the posterior thoracic arteries; and finally, the pectoral, which supply the pectoralis muscles and later terminate in the carotid, the vertebral, and the cervical arteries. The carotid artery gives off an esophageal artery. The other arterial trunk given off from the common aorta is the right brachio-cephalic or brachio-cephalic dexter (Fig. 61B, No. K, 18). The right brachio-cephalic artery gives off the subclavian, which continues as the axillary, and continues as the brachial artery. There is given off the anterior and the posterior thoracic, the right carotid (Fig. 61B, No. K, 11), the vertebral, and the dorsal. The last continues as the cervical.

FIG. 61B.

K. The arterial trunks. 1, The middle sacral artery. 2, The hypogastric artery. 3, The posterior mesenteric artery. 4, The ischiadic artery. 5, The femoral artery. 6, The renal artery. 7, The left pectoral artery or thoracico caudalis. 8, The left axillary artery. 9, The left carotid artery. 10, The left brachio-cephalic artery. 11, The right carotid artery. 12, The right brachial artery. 13, The right pectoral artery. 14, The common carotid artery. 15, The posterior aorta. 16, The celiac axis. 17, The anterior mesenteric artery. 18, The right brachio-cephalic artery. 19, The auricular portion of the heart. 20, The ventricular portion of same. 21, Sterno-clavicular artery. 22, Anterior thoracic.

L. The venous trunks. 1, The caudal vein. 2, The coccygeo-mesenteric vein. 3, The posterior mesenteric vein. 4, The anterior mesenteric vein. 5, The gastro-duodenal vein. 6, The portal vein. 7, The hepatic vein. 8, The left anterior vena cava. 9, The left pectoral vein. 10, The left brachial vein. 11, The left jugular vein. 12, The right jugular vein. 13, The right brachial vein. 14, The right pectoral vein. 15, The right anterior vena cava. 16, The posterior vena cava. 17, The common iliac vein. 18, The femoral vein. 19, The renal vein. 20, The internal iliac vein. 21, The hypogastric vein. 22, The auricular portion of the heart. 23, The ventricular portion of same. ]

The pulmonary arterial trunk is given off from the conus arteriosus of the right ventricle. It is guarded at its origin by three semi-lunar valves similar to those of the aorta. The trunk divides into two pulmonary arteries, which are short, one called the pulmonalis dexter and the other the pulmonalis sinister. The former goes to the right and the latter to the left lung. Each branch penetrates the lung near the bronchus. These arteries divide, or branch, similarly to the bronchi. Following the branchings of the bronchi, they finally terminate into the lung capillaries, forming networks on the bronchi and the air-tube terminals.

BRANCHES OF THE BRACHIO-CEPHALIC ARTERY

( Thyroidea ( ( Cervicalis inferior ( Vertebralis ( Vertebralis anterior ( ( Vertebralis posterior ( ( Arteria cervicalis ascendens ( Bronchiales ( Truncus ( Inferior esophageal ( caroticus ( Subcutaneous colli ( ( ( Carotis cerebralis ( ( Carotis ( Cervicalis superior ( ( communis ( Occipitalis ( ( ( Carotis externa ( ( Spinalis anterior ( Basilaris ( Cerebelli inferior Brachio-cephalic ( ( ( Clavicularis ( ( Sterno-clavicularis ( Sternalis ( ( ( Acromialis ( ( ( ( ( Subscapularis ( ( ( ( Ulnaris ( Subclavia ( Axillaris ( Brachialis ( Brachialis profunda ( ( ( Radialis ( ( Humeralis ( Circumflex humeralis ( ( ( anterior ( ( ( Thoracica externa ( Thoracalis ( ( Arteria thoracica ( Thoracica inferior ( longa ( ( Mammaria interna

( Circumflex humeralis posterior Brachialis profunda ( Collateral ulnaris ( Collateral radialis

The cord-like remnant of the ductus botalli, or embryonal connection between the lung arterial trunk and the anterior aorta, has been observed but is rare in grown birds.

The arteries, the veins, and the lymphatic vessels of birds anastomose far more frequently than those of mammals.

BRANCHES OF THE ARTERIA CAROTIS CEREBRALIS INTERNA

( Occipitalis ( Occipitalis sublimis ( ( Occipitalis profunda ( Meningea ( ( Temporalis ( ( ( Rete temporale ( Ophthalmica ( Recurrent ophthalmicum ( Rete ethmoidalis ( externa ( Ethmoidalis ( ( Plexus palpebralis ( ( Plexus alveolaris inferior ( ( Plexus muscularis Carotis cerebralis ( Plexus temporalis ( Plexus lacrimalis ( ( Ramus ciliaris posticus ( ( Meningea media ( ( ( Sphenoidea ( Ethmodalis ( ( Spheno-maxillaris ( Ethmoidalis ( externa ( ( ( Ophthalmica ( ( Ethmoidalis ( ( ( interna ( ( interna ( Cerebralis ( ( ( Ramus ( Sylviæ ( anterior ( Cerebralis profunda ( Choroid plexus ( Arteria centralis retinæ ( Ramus posterior

BRANCHES OF THE ARTERIA CAROTIS EXTERNA

( Hyoidea Carotis externa ( Laryngea superior ( Facialis ( Lingualis

BRANCHES OF THE ARTERIA CAROTIS FACIALIS

( Auricularis Facialis ( Facialis interna ( Alveolaris inferior ( Mentalis ( Maxillaris interna ( Facialis externa

BRANCHES OF THE CAROTID TRUNK

The =carotis communis= artery springs from the carotid trunk of the brachio-cephalic. It is directed horizontally, ascending to the ventral side of the neck. It then extends downward to the inferior median neck region. Just after leaving its origin it gives off several small branches to the bronchi and to the esophagus, and extends toward the head. The carotid lies on the thyroid gland and at this point touches the jugular vein (Fig. 21). At this point the =thyroid arteries= are given off from the carotid trunk. The thyroid gland also receives blood from the bronchialis artery.

Dorsalward and near the thyroid gland the carotid artery gives off a branch (the bronchialis) which accompanies the recurrent laryngeal nerve, along the inferior larynx and the bronchi, and supplies the lung substance and that part of the esophagus in this region.

The =vertebral artery= is given off from the carotid trunk, dorsalward to the thyroid gland, and on the left side. The right vertebral artery may be given off from the brachialis dextra or right brachialis.

The =inferior esophageal artery= is given off from the ventral side of the carotid, supplies the esophagus, extends then to the skin of the neck and to the trachea, is directed anteriorly toward the head and anastomoses with the vertebral artery. This artery accompanies the vagus nerve and forms a collateral artery to the carotid and the vertebral artery.

The =subcutaneous colli= springs from the carotid artery near the thyroid gland and communicates with the inferior cervical artery, which, in turn springs from the vertebral artery.