282 MR. AV. p. PYCRAFT ON THE [Api\ 15, 



articular surface for the otic head of the quadrate. Within it 

 lie several foramina and the mouths of two pneumatic cavities. 

 The foramina are the foramen ovale and the foramen rotundum, 

 the foramen for the 7th nerve, and the foramina of the sinus 

 petrosus. The pneumatic apertures are, as already stated, two 

 in number. The fii-st, and largest, opens into the mouth of the 

 tympanic cavity at its antero- ventral angle. It may be traced 

 inwards, and forwards, as a tubular recess leading into the para- 

 sphenoidal rostrum, terminating in the pituitary region. The 

 anterior wall of this recess — -the recessus tymjxini anterior — is 

 formed in its larger exterior portion, as is shown by Suschkin \ 

 by ossification of connective tissue extending in the young 

 skull between the alisphenoid above and the basisphenoid below. 

 When the Eustachian grooves are closed, they form two additional 

 and much smaller apertin^es, opening one on either side, into the 

 tympanic cavity, below the mouth of this anterior tympanic recess. 

 The second of these apertures is that of the posterior tympanic 

 recess. It is very small and not easily seen. If carefully looked 

 for, it will be found as a small hole, lying caudad of the foramen 

 ovale and foramen rotunda. It leads into a small pneumatic 

 cavity lying below the horizontal semicircular canal, and between 

 this and the inferior border of the lateral occipital wing. 



The sepai'ation of the squamosal and otic ai-ticular surfaces 

 for the quadrate by the aperture of the superior tympanic 

 recess is a point of some interest. In the Pala30gnatha3 tlie 

 recessus tympani superior is represented by a shallow cavity, lying 

 behind the articulation for the head of the quadrate. The I'oof 

 of the cavity is pierced by numerous small pneumatic apertures 

 leading from a mass of diploe lying between, and above, the 

 horizontal semicircular canal and the brain-case. The external 

 wall of this diploid tissue is formed by the parietal and lateral 

 occipital bones. In some Dinornithidje there is a small aperture 

 connected with this mass of pneumatic tissue lying iwfi'ont of 

 the articulation for the quadrate. In the Neognathfe the aperture' 

 of the superior tympanic recess lies — in Steganopodes, Tubinares, 

 and Sphenisci, for instance^in front of the quadrate articular 

 surface. But in the Accipitres and Striges, for instance, it 

 would seem that the separate anterior and posterior apertures, 

 lying on either side of the articular surface for the quadrate, in 

 the Dinornithida?, have here become confluent, and now form one 

 large aperture dividing the squamosal and otic articular siu-faces 

 for the quadrate far from one another. In the Sphenisci, by 

 reason of the great depth of the temporal fossa lying immediately 

 above, the greater part of this recess has become suppressed, only 

 the lower end now remaining. In the Pygopodes the relatively 

 greater depth of the temporal fossa, coupled with a general and 

 marked tendency for the suppression of pneumatic tissue through- 

 out the skeleton, have combined to obliterate the superior 

 tympanic recess altogether. 



1 " Zur Morptologie des Vogelskelets." Nouveaux Mem. cle la Soc. Imp. des 

 Naturalistes, 1899. 



