92 ANNALS NEW YORK ACADEMY OF SCIENCES 



Pterygoideus anterior (Pt. a.). — This short, strong muscle arises on 

 the ventral border and inner side of the quadrate, from the inter-orbital 

 floor, pterygoid and transverse. It has the typical reptilian insertion of 

 this muscle, wrapping around the posterior end of the articular. It is 

 inserted on the medial face and ventral border of the posterior fifth of the 

 mandible. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Depressor mandibulce (D. m.). — This muscle, the homologue of the 

 depressor of other animals, is called parieto-mandibularis by Osawa. It 

 is a large muscle which arises from the posterior border of. the parietal, 

 from the ligamentum nuchae, and to a slight extent from the squamosal. 

 It is inserted on the posterior face of the articular or on its retroarticular 

 process. 



ALLIGATOR 

 Plate VI, Figs. 5, 6 



In the alligator skull there is a great reduction of the posterior region 

 and a corresponding elongation of the antorbital region. The palate is 

 closed by the approximation of the secondary shelves of the maxillae, pala- 

 tines and pterygoids, so that the condition partly resembles that of the 

 mammals. The pterygoids are also very closely appressed, so that the 

 posterior internal nares are forced far to the rear and are almost ventral 

 to the articulation of the mandible with the quadrate. There has been a 

 progressive reduction of the temporal fenestras, so that the heavily roofed 

 skull of the alligator represents the specialized modern form of an ancient 

 order that had a much more open skull with large fenestrae and very 

 different proportions of the skull. The supratemporal fossa has been 

 reduced until it is almost rudimentary, while the rest of the posterior 

 region has also been encroached upon until the muscle space is quite 

 small. The quadrate has shifted' its position by inclining posteriorly, 

 giving the animals a much larger gape; the quadrate is fixed or moni- 

 mostylic. The auditory region is much changed by the secondary clos- 

 ing of the otic notch, so that the meatus appears to be in a different posi- 

 tion ; but this condition is merely the result of the closing in of the notch, 

 so that its original position is masked. The small size of the posterior 

 region of the skull and the corresponding reduction of the capiti-man- 

 dibularis is in a way compensated for by the great development of the 

 pterygoideus anterior muscle which has extended over the floor of the 



