7. A. sphenopalatina.—The sphenopalatine is one of the terminal branches of the internal maxillary; it passes mediad through the sphenopalatine foramen into the nasal cavity, and divides into numerous branches which supply the mucous membrane of the nose. It gives off just before it enters the sphenopalatine foramen the descending palatine (A. palatina descendens), which passes into the posterior palatine canal and emerges on the surface of the hard palate, where it ramifies.
8. A. infraorbitalis ([Fig. 120], o).—The infraorbital artery is a direct continuation craniad of the internal maxillary. It sends off numerous small branches to the teeth of the upper jaw, and a rather large branch which passes to the lower eyelid. It then enters the infraorbital foramen, at the same time dividing usually into two or three branches; these emerge from the foramen and supply the parts of the nose and upper lip adjacent to the foramen ([Fig. 131], r).
A. subclavia. The Subclavian Artery.
The left subclavian ([Fig. 118], c) arises from the convexity of the aortic arch just distad of the origin of the innominate artery, and about two or three centimeters from the heart. It passes craniad and slightly to the left, and turns into the left arm just craniad of the first rib.
The right subclavian ([Fig. 115], n) is a direct continuation of the innominate, the artery receiving the name subclavian after the right common carotid is given off, usually at about the level of the second or third intercostal space.
The subclavian has the following branches: the vertebral artery ([Fig. 118], g′), the internal mammary ([Fig. 118], h), the costocervical axis ([Fig. 118], g), the thyrocervical axis ([Fig. 118], j). Beyond the last-named branch it continues into the arm as the axillary artery ([Fig. 118], i; [Fig. 122], g).
Fig. 121.—Arteries of the Ventral Surface of the Brain.
a, A. vertebralis; b, A. spinalis anterior; c, A. basilaris; d, A. cerebelli inferior posterior; e, A. cerebelli anterior; f, A. cerebri posterior; g, cut ends of the two internal carotid arteries; h, cut ends of branches from the carotid plexus (g and h are placed within the circulus arteriosus or circle of Willis); i, A. cerebri media; j, A. cerebri anterior.
a. A. vertebralis ([Fig. 118], g′).—The vertebral artery arises from the dorsal surface of the subclavian opposite the first rib. It passes craniad and dorsad at the side of the thoracic portion of the longus colli muscle, and enters the foramen transversarium of the sixth cervical vertebra. It passes thence craniad through the foramina transversaria (which together form the vertebrarterial canal) and gives off at the intervertebral foramina branches to the muscles of the neck and branches which pass across the ventral surface of the spinal cord to join A. spinalis anterior. Craniad of the foramen transversarium of the atlas the vertebral artery turns dorsad in the groove on the lateral surface of the atlas. Here it gives off a large branch which passes laterodorsad to the muscles of the neck and may anastomose with a branch of the occipital artery. The vertebral artery then passes into the vertebral canal through the atlantal foramen. It passes to the ventral side of the spinal cord and unites at about the level of the foramen magnum with the vertebral artery of the opposite side ([Fig. 121], a) to form the basilar artery (A. basilaris) ([Fig. 121], c), which passes craniad along the ventral middle line of the brain. Just before their union the two vertebral arteries (a) give off each a branch which passes caudomediad. These two branches soon unite in the middle line, forming the anterior spinal artery (A. spinalis anterior) (b), which passes caudad the entire length of the spinal cord, lying on its ventral middle line and receiving many communicating branches from the vertebral, intercostal, and lumbar arteries.