8o DESCRIPTIONS OF PREPARATIONS. 



under surface the large para-sphenoid (P. S.), both developed in membrane. 

 Other membrane bones are the two nasals (Na.): the two praemaxillae 

 (P. Mx^} and the two maxillae (Mx^} which carry teeth in a simple series : 

 and the quadrato-jugals (Qu. y.) which continue the line of the maxillae 

 back to the distal ends of the quadrate cartilage (Qu.). The apertures of 

 the external nares (E. n.) lie just in front of the nasals. On the roof of the 

 mouth, in front of the sphen-ethmoid, are the two dentigerous vomers 

 ( F<0.) and at their anterior ends are the internal nares (7. n.). The palatine 

 bone (Pa.), an investing membrane bone, is here placed transversely a rare 

 position seen again in Ichthyosaurus : while the pterygoid (ft.) lies parallel 

 with the cranial axis. The latter is deeply forked behind : the outer process 

 underlies the quadrate cartilage : the inner or pedicle is continuous with the 

 quadrate and articulates with the ear-capsule. The squamosal (Sq.) is seen 

 in the lateral view. It is the homologue probably of the squamosal + the 

 praeopercular of bony Ganoids, two bones actually fused in Polypterus. 

 The complex stapes (St.) or columella auris, the homologue of the Perch's 

 hyomandibular ; the cartilage ring or annulus tympanicus (A. T.), the 

 homologue of the Ray's spiracular cartilage (?), which gives support to the 

 tympanic membrane, and the hyoid apparatus are not present in this 

 specimen (see p. 81, infra]. The lower jaw consists of the two typical rami. 

 The bulk of each ramus consists of an unaltered Meckel's cartilage (Mck.), 

 to which there is added distally an ossification known as the mento- 

 meckelian (M.Mck.) formed by the ossification of the lower labial cartilages. 

 Meckel's cartilage is covered in part by two membrane bones, one on the 

 outer side for a short distance of its distal part, the non-dentigerous 

 dentary (D.): the other on the inner side, the articular (At.) as it is termed 

 by Professor W. K. Parker, but identified formerly by Professor Huxley 

 as a representative of the angular, coronary and splenial elements of the 

 Sauropsidan lower jaw. 



The vertebral column numbers nine vertebrae and a urostyle. The 

 first vertebra is the only cervical vertebra : it is ring-like with a shallow 

 centrum, two concave facets for the occipital condyles and two post- 

 zygapophyses. The centra of the second to the seventh vertebra inclusive 

 are pro-coelous. The centrum of the eighth is amphi-coelous, and of the 

 ninth or sacral vertebrae biconvex anteriorly, the posterior surface being 

 divided into two facets for the articulation of the urostyle. The neural 

 arches are thin and narrow centrally, leaving in this region interspaces, 

 one between the other. The articulating processes or zygapophyses are 

 flat, and disposed normally. All the vertebrae except the first have lateral 

 processes tipped with cartilage and varying in length, size, and direction. 

 These appear to represent ribs fused to transverse processes. The urostyle 

 is long and curved. Its posterior end lies just above the cloacal aperture. 

 It is pierced laterally at its anterior end by the tenth pair of spinal nerves, 



