532 



DISSECTION OF THE BACK. 



External 

 branches : 



first three 



become 



cutaneous. 



Internal 

 branches, 



Vessels. 



Part of the 



occipital 



artery, 



which 

 gives a 



cervical 

 branch. 



Part of the 



vertebral 



artery. 



Deep cervi- 

 cal artery. 



Dorsal 

 arteries are 

 split into 



inner and 



outer 

 branches. 



and give 

 a spinal 

 branch. 



The external branches pass to the erector spinse, and supply it 

 and the intertransverse muscles. The first three pierce the erector 

 spinae, and become cutaneous after perforating the posterior layer of 

 the fascia lumborum. The branch of the last nerve is connected 

 with the corresponding part of the first sacral nerve by an offset 

 near the bone. 



The internal branches are furnished to the multifidus spinse 

 muscle. They are difficult to find, being contained in grooves on 

 the upper articular processes. 



VESSELS IN THE BACK. The vessels now dissected are the 

 occipital and the deep cervical arteries, a small part of the vertebral 

 and the posterior branches of the intercostal and lumbar arteries of 

 the aorta. Veins accompany the arteries. 



The OCCIPITAL ARTERY (fig. 192, a) courses along the occipital 

 bone. Appearing from beneath the digastric muscle, the vessel is 

 directed backwards under the sterno-mastoid, the splenius, and, 

 usually, the trachelo-mastoid, but over the obliquus superior and 

 complexus muscles. Behind the insertion of the sterno-mastoid it 

 becomes superficial, and ascends to the occiput, where it is dis- 

 tributed (p. 503). It supplies the surrounding muscles, and gives 

 the following branch to the neck : 



The princeps cervicis (fig. 192, 6) artery from the occipital 

 distributes twigs to the splenius and trapezius, and passing beneath 

 the complexus, anastomoses w r ith the vertebral and deep cervical 

 arteries. 



The VERTEBRAL ARTERY (fig. 192, c) lies on the neural arch of 

 the atlas, behind the articulating process, and appears in the 

 interval between the straight and oblique muscles. Beneath it is 

 the suboccipital nerve. Small branches are given to the surround- 

 ing muscles, and to anastomose with the contiguous arteries. 



The DEEP CERVICAL ARTERY (fig. 192, e) arises in common with the 

 superior intercostal artery from the subclavian. Passing backwards 

 between the transverse process of the last cervical vertebra and the 

 neck of the first rib, it ascends between the complexus and semi- 

 spinalis muscles, as high as the upper border of the latter, and 

 anastomoses with the cervical branch of the occipital artery. The 

 contiguous muscles receive branches from it, and anastomoses are 

 formed between its offsets and those of the vertebral. 



The POSTERIOR BRANCHES OP THE INTERCOSTAL ARTERIES pass 



back between the vertebrae and the superior costo-transverse 

 ligament, and divide like the nerves into inner and outer pieces. 



The internal branches end in the fleshy mass of the multifidus 

 spinee and semispinalis, and furnish small cutaneous offsets with 

 the nerves. 



The external branches cross beneath the longissimus dorsi, and 

 supply it and the ilio-costalis. Like the nerves, the lowest 

 branches of this set are the largest, and extend to the surface. 



As the dorsal branch of the intercostal artery passes by the inter- 

 vertebral foramen, it furnishes a small intraspinal artery to the 

 spinal canal. 



