OSSICTTLA AUDITUS I1ST THE HIGHER MAMMALIA. 
91.3 
internal surface. In the older embryoes the distal extremity of the long crus of the 
incus is flexed inwards, but has not any trace of the characteristic adult constriction. 
The orbicular apophysis cannot therefore be longer spoken of as a bone distinct from 
the long crus of the incus before or after birth, but is simply a small portion of the 
long crus separated by constriction from, and assuming a direction at right angles to 
it, accommodating itself in this way to the stapes. 
Embryonic history and adult condition of the stapes, together with the artery in 
connexion with it. 
This ossiculum appears contemporaneously with the cartilages in the arches and the 
cartilage surrounding the labyrinth; it lies dorsad of the sulcus tympanicus, ventrad 
of the seventh nerve and primitive jugular vein, external to the unperforated wall of 
the labyrinth with which at first it is not even in contact, and internal to the long crus 
of the incus (Plate 54, figs. 6, 7 ; Plate 55, figs. 12, 18 ; and Plate 56, fig. 24), with 
which it is much more closely connected, although from the different direction of its 
cells it cannot be described as being actually continuous with the hyoidean cartilage; 
it has the form of a circular ring of cells of uniform thickness. Through the centre of 
the ring passes a vessel (Plate 54, figs. 2, 6, 7, 9; Plate 55,figs. 12, 18; Plate 56, figs. 22, 
23, 24; Plate 57, fig. 27; and Plate 58, figs. 35, 36), which has never yet been described 
in the embryonic condition nor its value recognised in the formation of this ossiculum. 
True, Salensky has seen the vessel, but 'he describes it as being a branch of a vessel 
which he calls carotis interna, but which I have shown to be the primitive jugular or 
anterior cardinal vein. He also mentions that it ends in the mandibular arch. Otto 
(20) was the first to describe and figure this artery in the adult. He found it in the 
hybernating animals and imagined that some connexion existed between the course 
pursued by this vessel and the peculiar function of hybernation. Hyrtl (21) described 
it (at first unaware of Otto’s previous observations) in the Cheiroptera, Insectivora, 
the genus Lemur, and many Rodents. He named it the “ Steigbiigelarterie”; he 
found that it supplied part of the brain, the orbit and its contents, and the whole of 
the superior maxilla; he described also the homologue of this vessel in Man, which 
might have one of three sources— (a) the accessory middle meningeal, pursuing an 
unusual course; ( b ) the stylo-mastoid artery; or (c) a small branch from the anasto¬ 
mosis formed usually between the stylo-mastoid and vidiaa arteries. It has also been 
described by Meckel (22) in the Hedgehog and Dormouse, but called by him carotis 
interna, although doubtless it was this same vessel. This artery may be either free 
between the crura so that in the macerated skull no trace of it is left, or it may be 
surrounded by a bony canal which may have osseous union to one of the crura, so 
that a vertical bolt may occupy the space between the crura. This has been figured 
and named the pessulus by Carlisle (23) in the Marmot and Guinea Pig. He con- 
6 A 2 
