DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 151 
support the lower part of the deep uncinate chink, the nasal passage (7.p.). Over the 
out-turned hook of the section a mucous crypt, one of the many small distinct nasal 
glands (m.g.), are formed between the cartilage and the Schneiderian membrane. 
3rd Section (Plate 18, fig. 3).—This is from the hind part of the mobile, rooting 
snout, and here the upper lips begin to show themselves as depending lobes, the 
hollow of the palate now being more definite. Here the intertrabecula is as round as 
in an embryo Bird or a Shark; but here there has taken place what is not seen in the 
projecting part, the “rostrum,” in those very diverse Ovipara, namely, that the 
alinasal folds (a/.n.) are confluent with the foremost part of this precranial rod, which 
now takes the name of septum nasi (s.z.). Here each nasal tube is surrounded by 
cartilage, the alinasals having developed each into an almost complete tube, the lower 
part of which projects downwards far below the low wall of partition ; the two folds rise 
again, back to back, although they do not touch. Each sweeping fold of cartilage is 
indented infero-laterally, in correspondence with the form of the nasal passage, which 
is now trilobate ; a mucous crypt (see also fig. 2, m.g.) is seen outside the upper lobe. 
In several sections, between this and No. 2, the lower part of the ale nasi had 
joined back to back, and the whole snout was thus confluent in all its parts and 
formed a complete double tube, or non-segmented proboscis ; sections of other types 
(Mole and Shrew) well show this.* 
4th Section (Plate 18, fig. 4).—This is from behind the flexible snout, and now the 
investing bones, most of which were removed from the endocranium (Plate 17, figs. 1, 2), 
are seen in section as thin films of bone. The solid intertrabecula, with its crest, and 
the confluent aliseptal folds of the nasal labyrinth (a/.sp.), now form a strong septum 
nasi (s.7.). The alee are now free at their lower edge, but are enlarged there into a 
pedate process, which thrusts the lining skin inwards as a rounded lobe, looking 
downwards ; this is the first appearance of the inferior turbinal (7.tb.)—its fore end. 
The lower parts of the cartilage, towards the middle, are now free from the base of 
the septum (s.v.), their section is a hook, the lamina just bending outwards, then 
inwards, below, turning round to support JAcOoBsoN’s organ (/j.0.); here seen at its 
fore end. 
These curious submesial retral outgrowths of the ale nasi are the “recurrent 
cartilages ” (rc.c.). Between these are the front paired vomers (v’.), the bony part of 
this locally modified skeletal structure ; they converge below, and are thin uncinate 
splints (see Plate 17, fig. 1, 2’). 
The enlarging nasal passage (7.p.) gives off from its main, vertical part, two outer, 
and one inner, “horn,” the latter turning inwards, below ; here and there a mucous 
erypt is seen. 
The nasals (7.) and the premaxillaries ( px.) now come into view. Below, the fore 
part of the lower face is cut across, in front of the dentary, but through the basi- 
mandibular cartilage (b.mn.), here nearly circular in section, a tooth-pulp (¢.) is cut 
* The dotted line in fig. 2, shows where the cartilage is complete in the next section 
s 2 
