466 MR. W. OTTLEY ON THE GROUND-HORNB1LL. [Julie 3, 



plexus (8'), and, accompanying the inferior dental nerve, ends 

 in the mandible. After this the internal maxillary artery breaks up 

 into the maxillary plexus, which furnishes many branches to the 

 internal pterygoid and to the muscle which depresses the upper jaw. 

 The plexus is joined by a branch from the palatine artery (5), and 

 furnishes a large offset (19), which is partly distributed to the 

 olfactory mucous membrane, partly (23) ends by anastomosing with 

 the common trunk formed by the union of the palatine arteries. 



The next branch of the vertebral (6) is a small vessel which 

 supplies the internal pterygoid, and, turning across the spine behind 

 the pharynx, ends by joining its fellow of the opposite side. 



The next (5), the palatine artery, furnishes branches to the internal 

 pterygoid, and runs along the lower surface of that muscle. In front 

 it meets and joins its fellow, the left being considerably the larger. 

 The common trunk thus formed is joined by an offset from each 

 maxillary plexus, and soon breaks up into larger branches ; it is 

 distributed to the lower surface and the interior of the beak. 



The last branch of the vertebral, before it joins the comes nervi 

 vagi, is the lingual artery (3). This supplies the muscles above the 

 hyoid bone, and the mucous membrane of the mouth ; it joins its 

 fellow at the symphysis, and ends in the substance of the mandible. 



The obliterated carotid (car) is seen joining the vertebral, close 

 to the origin of the branch 10. 



After the internal carotid (21) has given off its branch to the 

 maxillary plexus, itruns along its canal to enter the skull on the side of 

 the sella turcica (vide fig. 3, p. 467); it at once sends a branch back- 

 wards (25), which probably anastomoses with that of the other side. 

 This vessel, the only representative of a basilar artery, runs backwards 

 in a groove on the upper surface of the basisphenoid, supplying the 

 medulla; the artery on the right side is considerably larger than 

 that on the left. The next large branches are distributed on the 

 outer surface of the optic lobes and the hemispheres ; and finally the 

 artery divides into the middle cerebral (28) and the ethmoidal (26). 

 The latter soon enters the orbit, where it has been already described 

 as anastomosing with branches 14 and 15. It helps to supply the 

 olfactory mucous membrane, and gives offsets to the bony expansion 

 on the top of the head and the skin in front of the eye (29). 



The principal differences between the arteries of the head in Bucorvus 

 and those of birds generally are therefore: — 1st, the absence of any 

 considerable superior thyroid artery ; this vessel is replaced by 

 branches from the comes nervi vagi. 2nd, the absence of any artery 

 which could be called facial. Its place is taken by branches from 

 the maxillary plexus and from the ophthalmic artery. It may be 

 added that Barkow calls that artery facial which, following 

 Bauer's description, I have named internal maxillary ; also that 

 the artery which Barkow names ethmoidal Owen calls ophthalmic, 

 and Bauer internal ophthalmic. In this case, and in the names 

 given to all the other branches to the head, I have used those which 

 were originally employed by Barkow. 



I have not attempted to suggest any theory to account for the 



