464 ARTERIES. 



Peculiarities. The length of the internal carotid varies according to the length of the neck, 

 and also according to the point of bifurcation of the common carotid. Its origin sometimes 

 takes place from the arch of the aorta ; in such rare instances, this vessel has been found to be 

 placed nearer the middle line of the neck than the external carotid, as far upwards as the larynx, 

 when the latter vessel crossed the internal carotid. The course of the vessel, instead of being 

 straight, may be very tortuous. A few instances are recorded in which this vessel was altogether 

 absent: in one of these the common carotid passed up the neck, and gave off the usual branches 

 of the external carotid : the cranial portion of the internal carotid being replaced by two 

 branches of the internal maxillary, which entered the skull through the foramen rotundum and 

 foramen ovale, and joined to form a single vessel. 



Surgical Anatomy. The cervical part of the internal carotid is sometimes wounded by a stab 

 or gunshot wound in the neck, or even occasionally by a stab from within the mouth, as when a 

 person receives a thrust from the end of a parasol, or falls down with a tobacco-pipe in his 

 mouth. In such cases a ligature should be applied to the common carotid. The relation of the 

 internal carotid with the tonsil should be especially remembered, as instances have occurred in 

 which the artery has been wounded during the operation of scarifying the tonsil, and fatal 

 hemorrhage has supervened. 



The branches given off from the internal carotid are: 



From the Petrous Portion . Tympanic. 



{Arteriae receptaculi. 

 Anterior meningeal. 

 Ophthalmic, 

 f Anterior cerebral. 



ET .7 n -. 7 r> ., Middle cerebral. 



From the Cerebral Portion { -r> ... 



I Posterior communicating. 



[ Anterior choroid. 



The cervical portion of the internal carotid gives off no branches. 



The tympanic is a small branch which enters the cavity of the tympanum, 

 through a minute foramen in the carotid canal, and anastomoses with the tym- 

 panic branch of the internal maxillary, and with the stylo-mastoid artery. 



The arterise receptaculi are numerous small vessels, derived from the internal 

 carotid in the cavernous sinus ; they supply the pituitary body, the Casserian 

 ganglion, and the walls of the cavernous and inferior petrosal sinuses. One 

 of these branches, distributed to the dura mater, is called the anterior meningeal; 

 it anastomoses with the middle meningeal. 



The Ophthalmic Artery arises from the internal carotid, just as that vessel is 

 emerging from the cavernous sinus, on the inner side of the anterior clinoid 

 process, and enters the orbit through the optic foramen, below and on the outer 

 side of the optic nerve. It then passes across the nerve, to the inner wall of 

 the orbit, and thence horizontally forwards, beneath the lower border of the 

 Superior Oblique muscle to the inner angle of the eye, where it divides into 

 two terminal branches, the frontal, and nasal. 



Branches. The branches of this vessel may be divided into an orbital group, 

 which are distributed to the orbit and surrounding parts ; and an ocular group, 

 which supply the muscles and globe of the eye. 



Orbital Group. Ocular Group. 



Lachrymal. Muscular. 



Supraorbital. Anterior ciliary. 



Posterior ethmoidal. Short ciliary. 



Anterior ethmoidal. Long ciliary. 



Palpebral. Arteria centralis retinae. 

 Frontal. 

 Nasal. 



The lachrymal is the first, and one of the largest branches, derived from the 

 ophthalmic, arising close to the optic foramen ; not unfrequently it is given off 

 from the artery before it enters the orbit. It accompanies the lachrymal nerve 

 along the upper border of the External Rectus muscle, and is distributed to 



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