. Journal of anatomy. rschordalis) (Pis. 1, 2). Anterior to the chorda! part comes (2), a part of vari-able breadth, but still of considerable breadth, which is formed fromtrabecule, and may be therefore designated the trabecular part (parstrabecularis) (Pis. 1, 2). This is followed anteriorly by a part whichposteriorly lies between the optic foramina, more anteriorly between theorbital cavities, and more anteriorly as the septum nasi. All these parts The Primordial Cranium of Microtus ampkiblus (Water-Rat) 311 taken togetlier form (3) the inferorbito-nasal septum (Pis. 1, 2, 9). Onto-genetica
. Journal of anatomy. rschordalis) (Pis. 1, 2). Anterior to the chorda! part comes (2), a part of vari-able breadth, but still of considerable breadth, which is formed fromtrabecule, and may be therefore designated the trabecular part (parstrabecularis) (Pis. 1, 2). This is followed anteriorly by a part whichposteriorly lies between the optic foramina, more anteriorly between theorbital cavities, and more anteriorly as the septum nasi. All these parts The Primordial Cranium of Microtus ampkiblus (Water-Rat) 311 taken togetlier form (3) the inferorbito-nasal septum (Pis. 1, 2, 9). Onto-genetically these parts all chondrify independently of one another in Talpa,Cavia, Tatusia novemcincta, and ? Homo. In the latter the trabeculse areformed quite independenth^ of the pars chordalis and of one another, but Ido not know if they arise independently of the interorbito-nasal septum. Although I have no specimen of Microtus young enough to statedefinitely that this is the mode of development in Microtus, yet it seems. Septum nasi. — ~ Pars interorbito-nasalis. Ala Eyeball. Trabecula. Medial wall of cochlear capsule duct. Pars chordalis. Clioida Text-fig. 1.—Talpa. Chondrocraniuni of 11-nim. embryo, viewed from below. justifiable to describe the central stem at the stage modelled on the samelines; and although no distinct traces of such subdivision are evident atthis stage, all being now fused, it is not difficult to indicate with someprecision their limits. Detailed Description of the Central Stem.—The chordal part of thecentral stem is roughly triangular in form as seen either from above or below(Pis. 1, 2). The basal region of this triangular plate forms the anteriorconcave margin of the foramen magnum. The apical region is markedby a small median foramen (PI. 1), the remains of the basi-cranial fenestra 312 Professor Edward Fawcett through which the chorda-dorsalis dips down from the dorsal aspect
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectanatomy, bookyear1867
