152 PROF. G. B. HOWES ON jacobson's [Feb. 1 7, 



sippiensis, in whicli I found the arese of the pre-palatine foramina 

 to be occupied by the two small sacs before mentioned (jc. 1, fig. 4), 

 the fibres of these vomerine ligaments could be traced to a connection 

 with both the membranous expansions closing the former and the 

 fibro-cartilaginous walls of the latter. The established doctrines of 

 morphology and the rules of precedent alike allow us to regard 

 these ligaments as the equivalents of the " missing parts," and to look 

 upon them and the sacs of the prepalatine foramina as the vestigial 

 remains of the palatine lobes of the vomers of Caiman nujer with 

 their associated structures. 



I have unfortunately been unable to obtain the head of a Caiman 

 niger in spirit ; but inasmuch as in a small C. sclerops of 125 centim. ' 

 I have found pre-palatine foramina to be present in a form identical 

 with ihatof Alligator mississipjiiensis, the conclusion formulated above 

 receives additional support. I find the pre-palatine foramina to be 

 present in most, but not all, of the skulls of Alligator mississippiensia 

 which I have examined smaller than the one afore dealt with in 

 detail (total length 112 centim.) ; while in the skulls of two adults 

 preserved in the Natural History Museum, which Mr. Boulenger 

 has kindly afforded me an opportunity of examining, I find (on the 

 left side of the one and the right side of the other) an insignificant 

 perforation which may perhaps be a last vestige of the prepalatine 

 foramen (?), but this is doubtful. It is clear, from all, that the 

 structures possessed by my specimen here figured (figs. 5 and 6) 

 when present must disappear with advancing age ; and it has yet 

 to be ascertained if their like is not to be found in other allied genera 

 and species. 



III. The only structure with which it is possiljle to homologize a 

 cartilaginous sac in intimate relationship with the prepalatine fora- 

 men of a Keptile is the Organ of Jacobson. This has of late years 

 received an exceptional amount of attention, Leydig has described ^ 

 its general features and relationships in certain Lacertilia, in that 

 masterly manner so peculiarly his own. Its more detailed characters 

 and origin have been incidentally dealt with by Born, in the course 

 of a series of lengthy monographs ^ devoted to a comparative study 

 of the nasal chamber and its ducts ; while Solger, "Wright, and others '' 

 have furnished details about it in certain reptilian forms. Concerning 

 the Crucodilia, its absence is everywhere proclaimed ; and Beard, 

 who has most recently investigated the facts of its early develop- 

 ment, specially states ' that he " searched for it in Chelonians and 

 in embryo Crocodiles, hut in vain." 



All recent inquiry has rendered it more and more clear that the 



' Tail broken ; measurement taken to posterior extremity of cloaoal orifice. 

 ^ Die in Deutschld. lebend. Arten d. Saurier. Tiibingen, 1872, pp. 96-99. 

 ^ Morph. Jahrb. Bd. ii. bis, viii. (1877-1883). 



* For a full bibliograpliy with detailed references, see Beard in Zoolog. 

 Jabrb. Bd. iii. pp. 778-780 (1889). 

 ° Loc. cif. p. 772. 



