104 MR. W. K. PARKER ON THE STRUCTURE AND 



space, and contains the rudiment of a hasioccipital hone (fig. 2) as a frail bony " cephalo- 

 style." 



The upper tract is of the same width at tHfe foramen magnum, but widens out, 

 wedge-hke, to the fontanelle ; it contains the rudiinent of a supraoccipital hone as a 

 shght endosteal deposit. 



The antorbital (lucillari/) tracts of the ethmoid are ossified (eth.), not, however, as 

 a "girdle-bone," but as in "Urodeles" as a pair of " sphenethmoids ; " these occupy 

 about three-fifths of the ethmoidal cincture — perfect here for a short distance. Below 

 (fig. 2), the two bones are separated by a distance less than their own width ; above 

 (fig. 1), they come a little closer together, ending there as sigmoid "horns," turned 

 forwards till they nearly touch the conchoidal nasal roof 



These bones, laterally, just run round the end of the long oval iiiterorbital fenestra ; 

 in their interspace below there is between these two ecto-ethmoids an evident, endosteal, 

 " mesethmoidal " tract like the azygous endosteal patches in the hind skull. 



Here, once more, we come athwart the familiar " perpendicular ethmoid," and the 

 basi- and supraoccipital bones. 



The palato-suspensorial arches have thin bony plates (j^o., 2^9-)> ^^'^ these, as well 

 as the bones that surround the face, are normal, if comj)ared with a young Common 

 Frog of the first summer. 



The vomers (fig. 2, v.) are small and toothless; the parasphenoid (pa.s.) is narrow, 

 especially in the fore part, yet it is, essentially, typical. But the fronto-parietals 

 (fig. l,y"/>.) are by far the slightest and most delicate I have yet seen : they reach to 

 the conchoidal nasal roof in front, and partly cover the anterior canal (a.s.c.) where 

 these needle-like bones become roughly pedate. These bones only cover the outer edge 

 of the arrested lateral rudiments of the " tegmen cranii." 



The nasals and the squamosals («., sq.) are under-sized but quite normal ; so also 

 are the parts of the mandible (fig. 3), and the hyo-branchial plate with its processes 



(fig- 4). 



The aniudus (fig. 1, ci.ty.) is open above and rather small. The stylo-hyal (at.h.) is 

 articulated, above ; the Eustachian passage (eu.) is of medium size and reniform, with 

 the concavity looking outwai'ds and backwards. 



The stapes (fig. 5, t>t.) is between a lozenge and an oval in shape ; it is large, and 

 has a short stalk. 



The cartilaginous enlargement on the oblique end of the columella is not segmented 

 off as a distinct inter-stapedial. The medlo-stapedial [m.st.) lessens rapidly from this 

 cartilaginous process, and ends as bone, a little behind an oval, decurved, thick but 

 smuW, foot of cartilage — the extra- stapedial (e.st.) ; there is no ascending process from 

 this lobe. The labial cartilages {i(.I\ii.l'-.) are normal. Many of the things that dis- 

 tinguish this from the typical skull depend upon arrest, and are such as can be seen in 

 a young Common Frog, five or six months old. 



