THE INGUINAL PLEXUS 353 



It may be mentioned that a slender vascular plexus lies between the distal parts of 

 the common carotid artery and the internal jugular vein, close to the origin of the 

 pterygo-maxillary and internal carotid arteries. This rete drains into the internal 

 jugular vein. There is indeed a high degree of vascularity in all the tissues around the 

 base of the skull and the cranial part of the neck region. The general tendency of the 

 venous channels in the Fin Whale to a plexiform disposition has already been noticed, 

 and has been observed in Cetacea by other authors (Owen, for the Porpoise). 



RELATION TO NERVES 



Among the vascular networks of the basicranial rete there is a complex of fine nerves 

 taking origin from the trigeminal. A special retial branch leaves the fifth nerve at its 

 point of emergence from the cranium immediately in front of the tympanic bulla and 

 passes in a caudal direction (Fig. 9), ventral to Meckel's cartilage, distributing nerves 

 to the surrounding vascular capillaries. Further branches to the rete leave the fifth 

 nerve before its emergence from the skull and accompany it through the fenestra. 



SUMMARY 



The basicranial rete lies at the base of the skull in a cavity between the articulation 

 of the mandible and the tympanic bulla. It is bounded by the internal pterygoid, 

 palato-glossus and middle constrictor muscles. 



It receives numerous fairly stout branches from the external carotid artery, cervico- 

 facial of Turner, and drains into the pterygo-maxillary vein. 



It is innervated from the trigeminal nerve. 



One of the chief features of the basicranial rete is its separateness from surrounding 

 structures. It is invested by a connective tissue integument, and can be dissected away 

 from surrounding muscles. Like the thoracic rete, however, it possesses its own 

 arteries, veins and nerves, and does not lie upon the direct course of any main blood 

 vessel. It is, indeed, even more discrete and compact than the thoracic rete, and the 

 vessels that supply it are distinct and separate vessels to an extent even more marked 

 than in the thoracic rete. Judging from the disposition of the arterial supply and 

 venous drainage, it may be suggested that the blood which enters the rete is entirely 

 arterial and the rete, unlike the thoracic one, is an entirely arterial structure. The 

 thoracic rete, as already indicated, is partly arterial, but from its arrangement would 

 appear to be to a larger extent venous. Blood must be supposed to enter the basicranial 

 rete from the cervico-facial artery and to leave it by subsidiary veins draining into the 

 pterygo-maxillary vein. 



THE INGUINAL PLEXUS 



A large vascular network is situated in the inguinal region and appears to be intimately 

 related to the inguinal lymphatic glands. It is not proposed to employ the term " Rete 



Mirabile" for this plexus, since its appearances suggest a difference in nature from 



4-2 



