DEVELOPMENT OF THE SKULL IN THE PIG. 



315 



within, above, and below (figs. 1, 2, 5, 6, au.\ but as a mass they are not much changed 

 from the last stage. 



In the sectional view (fig. 5) the Eustachian tube {eu.) is seen below the basisphenoid 

 {h.s.)\ below the soft palate the ceratohyal (c.hy.) is cut through, and along the inside 

 of the lower jaw the primary mandible is seen. This is better shown when dissected 

 out (fig. 7) ; and now its malleal end is ossified (this part is cut through in fig. 1), whilst, 

 below, the Meckelian commissure is severed, the bars uniting along their anterior 

 fourth. I can only find one osseous centre here in the mandible, the dentary (d.) ; this 

 is found in the rapidly chondrifying nidus, which, like a huge " inferior labial," obliquely 

 overlaps the primary mandible ; in Man, according to Callendee, there is an osseous 

 centre at the chin in Meckel's cartilage, and a second splint (splenial) on the inner face 

 of the dentary (see Phil. Trans. 1869, Plate xiii. figs. 6 & 7, p. 170). 



A few of the many sections prepared of this stage will now be described, and they 

 will thoroughly explain the structure of the parts which have above been described 

 mainly from dissections. 



The ^rsf is through the snout (Plate XXXIV. fig. 8), and shows the arched cartilages, 

 united together in front, which were formed by fusion of the alte nasi with the overbcnt 

 trabecular horns. 



The second (Plate XXXIV. fig. 9) is through the alae nasi (al.n.), fore part of septum 

 (s.n.), alinasal turbinal (al.tb.); and the masses with trilobate outline below are the 

 recurrent trabecular horns (rc.c). 



The third section (Plate XXXIV. fig. 10) shows a curious triradiate cartilage separated 

 from the "alse nasi;" this is the "appendix" (a.al.n.); here the trabecular cornua are 

 becoming slenderer. 



The fourth (Plate XXXIV. fig. 11) shows the same parts further back; here the 

 recurrent process has become a smallish band lying flat on each side of the base of 

 the septum, which is now becoming high, but has not commenced the inferior turbinal 

 fold. The four-winged section, on each side, below the septum and recurrent cartilages 

 is the severed premaxillary see also fig 2). 



The fifth (Plate XXXIV. fig. 12) is through the middle of the inferior turbinal [Lth.) ; 

 the pedate section here shows the upper limb coiled on itself, but not the lower at present. 

 The recurrent laminae of the trabecular horns are running even past this point backwards ; 

 they are here vertical, and in close relation with the nidus of the scoop-shaped vomer (v.)*. 

 In this section the outer stratum of granular tissue overlying the nasal canals is now ossi- 

 fied as the nasal bones (n.), and the mass of tissue overlying the pterygo-palatine bar has 

 become the maxillary (jnx.), with its deep dental groove and pulps and its palatine plate. 



The sixth (Plate XXXIII. fig, 4) section is through the solid anterior third of the 



* The relation of these recurrent developments of the trabecular horns to the splints that belong to the first 

 facial arch is of intense interest; I am working out this subject in various groups; it is most complicated in 

 Passerine Birds, " ^githognathse " (H.). They are evidently formed by the fusion of a "labial" with each 

 trabecular horn. If we add to this the "appendix alac nasi" and the secondary mandible, we get three pairs 

 of suctorial cartilages in an ordinary Mammal. 



2 t2 



