58 ANATOMY OP THE HEAD AND NECK. 



three inches has been observed. It will be seen that when 

 such is the case, the thoracic cavity might easily be opened 

 in the course of any operation in this locality. 



The subclavian artery gives origin to the following 

 branches, viz: 



Vertebral, Internal Mammary, 



Thyroid Axis, Superior Intercostal. 



The vertebral artery, the first and largest of the branches, ascends 

 the neck upon the transverse processes of the cervical vertebrae until 

 it reaches the sixth, when it enters the vertebral foramen and follows 

 the caual formed by these foramina as far as the atlas ; having passed 

 through the foramen of the atlas, it curves around its articulating pro- 

 cess, perforates the posterior occipito-atloid ligament, as well as the dura 

 mater, and enters the foramen magnum to unite with the vertebral of 

 the other side in forming the basilar artery. In the canal it lies in . 

 front of the anterior trunks of the cervical nerves, except the first and 

 second, the former of which it crosses on its inner, the latter on its 

 outer side. In its course the vertebral artery gives off branches to the 

 membranes of the spinal cord and the deep muscles of the cervical 

 region, and a posterior meningeal branch to the posterior fossa of the 

 cranial cavity and falx cerebelli. Occasionally this artery does not 

 enter the vertebral foramen till it has reached a point higher than the 

 sixth vertebra. The arteries of the two sides may vary in size, in 

 which case it is ordinarily the left which is largest ; one of them 

 may also, as has been stated, arise from the aorta ; this irregularity 

 has rarely been noticed except upon the left side. 



The thyroid axis springs from the subclavian, close to the inner side 

 of the scalenus anticus muscle ; it does not always exist, as the 

 branches to which it gives rise are not unfrequently given off directly 

 from the subclavian; they are the 



Inferior thyroid, 

 Supra-scapular, 

 Transversalis cervicis. 



The inferior thyroid artery, a vessel of considerable size, passes ob- 

 liquely inward, behind the common carotid, to the thyroid body, which 

 it penetrates at its posterior surface, and in the substance of which it 

 anastomoses with its fellow of the opposite side, and with the supe- 

 rior thyroid, a descending branch from the external carotid ; in its 

 course it supplies a branch called the anterior cervical to the posterior 

 aspect of the trachea. The place of this artery is sometimes taken by 

 a trunk called the middle or lowest thyroid, or thyroid of Neubauer, and 

 which, springing from the innominata or the aorta, ascends in front of 

 the trachea to the lower part of the thyroid body. This branch may 

 be present also without the absence of the inferior thyroid. 



The supra-scapular artery is a large branch which passes outward, 

 behind the clavicle, to the scapula, where, crossing the supra-scapular 

 notch, it is distributed to the dorsum of the scapula, as is described 

 in Part Second, Dissection VI. 



The transrersaliit cervicis artery, also a large branch, crosses the neck 

 higher than the preceding, and divides into two branches, the superjl- 



