312 



ME. W. K. PAEKEE ON THE STEUCTUEE AND 



lently illustrated by the late Dr. Eschricht Ni Tavler til Oplysning af Hvaldyrenes 

 Bygning, udferte til utrykte Foredrag af afdede Etatsraad Dr. D. F. Eschricht :" Copen- 

 hagen, 1869. Edited by Professor Reinhardt, plate ii. figs. 1-3). 



The well-marked granular territories that at first invested the primordial skull and 

 face are now largely ossified, and these ossifications are massive in relation to so small a 

 skull. As in the strong-legged " Herbivora " generally, and in the "Aves prsecoces," 

 the development before birth and before hatching is very rapid, so that they are strong 

 and in good liking at their first appearance. Moreover, the primordial parts are 

 undergoing endostosis at many'points, and from this time the bony metamorphosis takes 

 place very rapidly. If this skull (Plate XXXIV. figs. 1-7) be compared with that of 

 the Bird (" Fowl's Skull," Plate lxxxiv.-lxxxvii.), it will be seen that the premaxillaries 

 (ji.v.) do not reach to the end of the snout, instead of projecting beyond it, and they do 

 not send a nasal process between the nasal bones up to the frontal. Here, in the 

 Mammal, the maxillary is by far the largest bone, and, with the linking malar and 

 zygomatic spur of the squamosal, forms a strong subocular arch, one pier of which is 

 formed by the maxillary and reaches near to the nostril, whilst the other pier is formed 

 by the supratemporal and stretches over the auditory capsule to the occiimt (Plate 

 XXXIV. fig. l,mx.,j., z.sq.). This sigmoid, trilobate temporal (squamosal) bone, besides 

 creeping over the infero-lateral wall of the cranium by its squamous part, clamping the 

 outer wall of the ear-capsule by a long falcate process, and perfecting the great facial 

 yoke (zygoma), also takes in a new relation ; it articulates with a Avell-differentiated 

 secondary mandible [d). This is distinctively Mammalian ; for in the highest Sauropsida 

 (the Bird) the primordial and secondary mandibles have an equal development, and are 

 permanently combined as the free arch of the mandible, the large "pier" of which 

 is merely the hugely developed head, neck, and shoulder of the first mandibular rod. 

 In this stage of the Mammalian skull we catch the equivalence of these primary and 

 investing parts ; but the new hinge is formed already, and the primary bar, now at 

 its highest relative development, shows no sign of segmentation into a pier (quadrate) 

 and a free arch (articulo-Meckelian). By the time of birth, the whole of the large 

 succulent rod of cartilage which runs along the inside of the lower jaw (fig. 7, d., mk., m.) 

 and coalesces largely with its fellow in front will have shrunk up into a delicate fibrous 

 band, leaving a small bony style (processus gracilis) to the arrested upper part of the 

 rod*. A bony ring is growing round both the preoral and the first postoral clefts; 

 these are the lacrymal (/.) and the tympanic (ty.); the first of these has an outer facial 

 development, and is not hidden in the orbit as in Man. The nasal, frontal, and parietal 

 bones (?^, |;.) form a regular double series; they are only equivalent to the ijincr 

 layer of the scutes seen in the same region in Ganoid Fishes ; yet they are very thick, 

 the thickness depending upon the free development of connective (indifferent) tissue 

 between the cutis and the primordial skull. Tlie fontanelles are still wide open ; but 



* In the figure (Plato XXXIV. fig. 7, </.m/,:) the primary rod is cut tlirough, and the mandible detached 

 from its new hirge these jails will be described more in detail from the figures of sections. 



