OF THE SKULL IN THE AMPHIBIA UEODELA. 167 



tooth-tract (v), and by a small semioval cartilage behind. This is the " ethmo-palatine " 

 element, a rudimentary preoral bar (fig. 1, behind no). The base of this small, but im- 

 portant rudiment 19 attached to the most outbent part of the trabecula ; its apex looks 

 directly outwards. 



Besides this antorbital rudiment, there is a large postorbital cartilage in union with 

 this simple chondrocranium. This is the suspensorium, whose free part is the quadrate, 

 with its condyle (q). The suspensorium is half the size of the ear-capsule ; it is a trifur- 

 cate cartilage. The longest and slenderest of the forks is the " ascending process " (a.p) ; 

 its direction is inwards, upwards, and a little backwards ; it has coalesced with the trabe- 

 cular crest near its top, and forms a bridge over the first or orbito-nasal branch of the 

 trigeminal nerve (5 1 ). 



The next fork is the "otic process" {ot.p); it grows directly backwards, and clings 

 like a snail's foot to the outside of the ear-sac, embracing, by its pedate end, the ampulla 

 of the horizontal canal. The third fork or, rather, descending cms is the quadrate region 

 of the suspensorium (</) ; it grows forwards, so as to end opposite the middle of the inter- 

 orbital region, and outwards from the skull to a distance equal to the width of the 

 skull. The oblique end is scooped a little on its upper face for the mandible (fig. 1) ; the 

 articulation is made at right angles with the long axis of the skull. These are all the 

 chondrified parts that form this simple skull; yet, few as they are, the elements are 

 diverse in nature. 



The parachordals and the trabecule are most probably homologous tracts ; but the 

 sense-capsules and the antorbital and postorbital cartilages belong to two other cate- 

 gories ; the former are paraneurals, and the latter are visceral or facial arches. 



Before passing to the lower parts of the face I must remark upon a change that has 

 begun in the ear-capsule. The walls of this sac had become well chondrified ; but a 

 remarkable cleft has appeared on its under surface, nearly in the middle. The cleft is 

 the rudimentary "fenestra ovalis " (fs.o), and the thin ragged edge of cartilage that now 

 imperfectly hides the enclosed otolith is the rudiment of the stapes, not yet severed from 

 the capsule *. 



The manner in which the fast-growing capsule literally bursts is very remarkable ; the 

 dehiscence gives rise to a triradiate opening, and in the hinder part of the space there is 

 a thick ingrowth of the outer wall, which passes into the vestibule upwards and forwards, 

 and forms a partial irregular septum (fig. 2, fs.o) to the capsule. 



As the Urodeles are the fathers of all those that prepare a movable stapes for the more 

 accurate transmission of the waves of sound, the mode of growth of this part in them is 

 of the greatest interest. 



The lower arches (PI. XIV. fig. 3) are shown in relation ; in the first two the upper 

 element, or suspensory part, is not shown; that of the first has coalesced with the skull; 

 that of the second, the hyomandibular, is suppressed in most of the " Caducibranchs " and 

 in some of the " Perennibranchs," e. g. in Menobranchus. This is a correlate of the early 

 closing-in of the first cleft ; in no Urodele that I have seen is there the same degree of 



* For a Ml description of the formation of the fenestra ovalis and stapes, see my recent memoir on the skull of 

 the Urodeles in the ' Philosophical Transactions ' for the year 1S77. 



23* 



