360 



itself towards the outer surface. The coat of enamel thus presents a deep angular fold pene- 

 trating from the outer side of each plate or lobe of dentine. These lobes are united together 

 by a thick layer of cement, which substance also fills the enamel folds. The last molar is 

 much larger than the rest, and consists of a greater number of enamelled dentinal plates ; of 

 these, the first only resembles the folded dentinal lobes of the antecedent molars ; the rest 

 are simple, broad lamellae, placed not quite transversely, the outer border being more back- 

 wards than the inner one ; there are eleven of these plates in addition to the first folded plate, 

 and the outer border of the last plate is reflected inwards, forming the rudiment of an addi- 

 tional plate. The sides of the large and deep socket of the last molar are grooved for the 

 reception of the transverse plates, which are cemented together by thick layers of cement ; in 

 the lower jaw the three anterior grinders are larger, and the fourth is smaller than those above : 

 the premolar consists of three grooved or inflected plates of dentine with the enamelled fold 

 penetrating their inner surface ; the next tooth consists of three similar lobes, but the fold 

 penetrates the outer surface of the third lobe. The third and fourth grinders each consist of 

 four lobes of dentine, the first and fourth lobes being grooved, the second and third being 

 simple plates ; the groove enters the inner side of the first and the outer side of the fourth 

 lobe. Bristles are passed through the bony canals which open into the back part of the 

 prepalatine foramina. 



Hunterian. 



1976. The skull of a Capybara (Hydrochverus Capybara), vertically and longitudinally 

 bisected. 



It is nine inches in length. The elements of the occipital have coalesced, and the basi- 

 occipital has coalesced with the basisphenoid. The pterygoids are excavated by large conical 

 sinuses, with an obtuse apex directed upwards and forwards ; the sinus being formed ante- 

 riorly by the proper pterygoids, and posteriorly by the ecto- and ento-pterygoid plates of the 

 sphenoid. The ectopterygoid plate is perforated by a canal, answering to the interpterygoid 

 canal of the Agouti, above which is a smaller ectocarotid canal. The process from the squa- 

 inosal, which articulates with the maxillary tuberosity, also articulates with the pterygoid and 

 ectopterygoid process external to the canals above described. 



Presented by Prof. Owen, F.R.S. 



The following are parts of the same skeleton of the Capybara. 



Presented by the Zoological Society of London. 



1977. The skull, with the calvarium removed, and the teeth of the left side shown in 

 their sockets. 



The basisphenoid is perforated by a median vertical canal, and is notched laterally by the 

 entocarotids. The cribriform plate and its median ridge or ' crista galli ' project backwards 

 into the large rhinencephalic fossa. There is no interparietal. 



1978. The lower jaw, with the teeth on the left side similarly displayed. 



