62 



THE OSTEOLOGY AND MYOLOGY 



vomerine knob betraying the passage of the optic nerve into the orbit. The cribriform 

 plate of the ethmoid begins at the anterior base of the inter-orbito-sphenoid process of the 

 bone, and thence curves upward as it passes forward, in nearly the quadrant of a circle, thus 

 finally gaining the top of the bone, and almost or quite touching the inside of the frontal. 

 At its lower part the sieve is flat from side to side ; more anteriorly and superiorly it is 

 transversely concave. It is pierced with innumerable foramina, of varying size, but all 

 small, very evenly distributed over its whole surface, with no indication of a median divid- 

 ing line, except just at the antero-superior extremity, where there is a very small space free 

 from holes, and also a slight projecting point — obviously a rudimentary crista galli. The 

 lowermost foramina lead obliquely downward as well as forward ; the upper ones directly 

 forward ; the different lamina3 of the spongy substance having corresponding direction. It 

 would be difficult, even were it desirable, to describe the details of the spongy convolutions : 

 suffice it to say that they form lai-ge masses on either side of the median plate, correspond- 

 ing in contour with the latter, and consist of very numerous exceedingly thin laminae, 

 mostly Ijdng flatwise, and running from behind forward, partitioning each half of the nasal 

 chamber into numerous small inter-communicating passages, each of which is lined by a 

 duplicature of the common mucous membrane under which the olfactory nerves ramify. 

 Upon the posterior and external part of the under surface of each spongy body the laminte 

 unite to form one continuous thin plate, that directly roofs that part of the nasal passage ; 

 more anteriorly, and toward the median line, the same surface comes in apposition with the 

 spongy mass that is attached to the inside of the superior maxillary ; and along this part of 

 it there is no such coalescence of the extremities of the laminae into one smooth plate ; the 

 under surface of the maxillary sponge (inferior turbinate bone) continuing forward the roof- 

 ing of the nasal passage. Not 

 as in those mammals in which 

 the ethmoid takes part in the 

 formation of the orbital wall, 

 and in consequence develops, 

 by external coalescence of its 

 laminae, a smooth surface (" or- 

 bital plate of ethmoid," e. g., in 

 man) the lateral surface of the 

 spongy mass does not present a 

 continuous osseous plate ; it 

 shows throughout the edges of 

 the laminae, penetrating its sub- 

 stance, and the duplicatures of 

 the mucous membrane ; and lies 

 wholly inside the lateral plate 

 of the frontal, vertical plate of palatal, and orbital plate of lachrymal, which three together 

 form the inner (mesial) wall of the orbital cavity. 



In the mandible (fig. 7, lateral view, left side ; fig. 8, from above) all traces of the sev- 

 eral bones of which it may have been originally composed, disappear at an early period ; 

 each lateral moiety was found entire in the youngest specimens examined. At the same 

 time, the union of the halves always remains a simple synchrondrosis ; and the jaw 



Fig. 7. 



Tw. 8. 



