THE COMMON CAROTID ABTEEIES. 577 



Preparation of the arteries of the head. — After carefully removing the skin, dissect the 

 superficial arteries of one side— that is, the external maxillary, niaxillo-muscular, the 

 temporal trunk, and the posterior auricular arteries, excising the parotid to expose tlie 

 origin of the three last-named vessels. On the opposite side, the deep arteries are 

 prepared, after disposing of the branch of the maxilla, as in the preparation of the 

 muscles of the tongue ; the orbital and zygomatic processes being removed in three 

 sections with the saw, as in figure 286, which will serve as a guide in the dissection of 

 all these arteries. 



OCCIPITAL AETEEY. (Fig. 286, 6.) 



_ The occipital artery is a slightly flexuous vessel, lying beside the upper 

 third of the internal carotid. It ascends beneath the transverse process 

 of the atlas in passing behind the guttural pouch, between the maxillary 

 gland and the straight anterior muscles of the head. It then insinuates 

 itself between the small lateral straight muscle and the inferior arch of the 

 above vertebra, to pass through its anterior foramen, and terminate by two 

 branches, after coursing along the short fissure which unites this foramen 

 with the superior. In its track, this artery is crossed, outwardly, by the 

 pneumogastric and spinal nerves, and the occipital nerve of the great sym- 

 pathetic, and is accompanied by the divisions of the inferior branch of the 

 first pair of cervical nerves. 



The two terminal branches of the vessel are the ocdpito-muscular and 

 cerebrospinal arteries. 



The collateral branches are three in number, and in the order of their 

 emission are named : 1, The prevertebral artery ; 2, The mastoid artery ; 3, 

 The atloido-muscular artery. 



CoLLATEEAL BRANCHES. — 1. Prevbetebeal Arteey (Fig. 286, 9). — The 

 smallest of all the branches emanating from the occipital, this artery is 

 detached at a very acute angle, and immediately divides into several 

 filaments, some muscular, the others meningeal. The majority of the first 

 pass between the oceipito-atloid articulation and the small anterior rectus 

 muscle of the head, and expend themselves either in that muscle, or the 

 great rectus ; the second, generally two in number, are always very slender, 

 and reach the dura mater by entering, one through the posterior foramen 

 lacerum, the other by the condyloid foramen. 



2. Mastoid Arteey (Fig. 286, 8) . — This vessel arises at an acute 

 angle above the preceding, and goes towards the mastoid foramen by 

 creeping on the external surface of the styloid process of the occipital bone, 

 beneath the small oblique muscle of the head. It enters the parieto- 

 temporal canal by this foramen, to anastomose by inosculation with the 

 spheno-spinous artery. 



In its course it describes a curve downwards, and throws off a large 

 number of collateral branches. Among these are some which originate 

 before the artery enters its bony canal, and which are destined for the 

 muscles of the nape of the neck. Others arise in the interior of this canal, 

 and escape from it by the orifices that cribble the temporal fossa, to expend 

 themselves in the temporal muscle. Some ramuscules reach the dura mater. 



We have seen the mastoid artery arise directly from the common 

 carotid, and furnish a parotideal branch. 



3. Atloido-musculae oe Eeteogradb Aeteey (Fig. 286, 7). — This 

 branch is not constant, and when it does exist it presents a variable volume. It 

 is detached from the occipital, underneath the transverse process of the atlas, 

 by forming with the parent branch a right, or even an obtuse angle ; it is 

 directed backwards, traverses the inferior foramen of the process of the 



