158 ON jacobson's organ in the crocodilia. [Feb. 1 7, 



those already described {ante, p. 151) concerning its relationship to 

 the vomerine ligament {Ig., fig. 4), show it to be a secondary- 

 outgrowth, arising in correlation with the shortening up of the vomer, 

 and having little, if anything, to do with the palatine process as 

 ordinarily understood. 



VI. Parker, in his monograph on the development of the skull in 

 the Crocodilia, described ^ the early differentiation of a basi-mandi- 

 bular cartilage, such as he had previously encountered ^ in the embryo 

 of Chelone viridis. He states, on the authority of Prof. C. Stewart, 

 of the R. College of Surgeons, that in the embryo Crocodile the 

 conjugated distal ends of the mandibles (Meckel's cartilages) become 

 dilated. My friend Mr. Boulenger has recently called attention in 

 these 'Proceedings' ^ to the existence of a small bone in the mandi- 

 bular symphysis of Heloderma ; and he inclines towards asso- 

 ciating it with the mento-Meckelian bones, well known to occur 

 in the living Anura. The latter (m.m., fig. 8) arise as ossifications 

 of the Meckelian cartilages, and the distal ends of those rods gene- 

 rally unite, in these animals, to form a prominent mass which 

 may exactly correspond to the symphysial cartilage of Stewart. I 

 have long been familiar with the fact that in some Anura (ex. Hi/la 

 cartdea, fig. 8) this (m.b.) may become segmented off in the manner 

 of the basal cartilages of the postoral visceral arches of the lower 

 Ichthyopsida, and of the cartilage described by Parker in the young 

 embryos of Crocodilus and Chelone; it would therefore appear to be 

 altogether independent of the mento-Meckelian bones. 



The existence of this "basi-mandibular " element of the mandi- 

 bular arch is not without interest, in view of the belief in the serial 

 homology between the latter and the postoral skeletal arches *. 



During this investigation I have had the good fortune to have been 

 repeatedly in conference with my friend Mr. Boulenger ; and my best 

 thanks are due to him for having, by his valuable assistance and 

 advice, rendered my task, in itself pleasurable, doubly so. 



EXPLANATION OF PLATE XIV. 



Fig. L Crocodilus palustris. Median longitudinal section through nasal region 



of dried skull. One-third not. size. 

 Fig. 2. Caiman niger, dried skull. A similar section to fig. 1, cut to the right 



of the middle line. One-third nat. size. 

 Fig. 3. Lepus cuniculus. Dissection of inner portion of olfactory capsule of left 



side ; to show the vomer and other supporting elements, in relation to 



the organ of Jacobson. Twice nat. size. 



1 Trans. Z. S. vol. xi. p. 280 (1883). 



» Challenger Eep. Zool. vol. i. pt. 5, p. 20 (1880). 



* Above, p. 111. 



* Cf. Huxley, Journ. Anat. and Phys. vol. x. pp. 421 & 427 (1876) ; and 

 Parker, oj>. cit. White has recently recorded the existence of a basi-maadibular 

 cartilage in Lcemargus (Anat. Anz. 1890, p. 260). 



