162 
Journal of Agricultural Research voi. xxvi, No. 4 
series of increasing defectiveness. Twelve grades, based on external 
appearance, have been used. These are shown somewhat diagram- 
matically in figure 1. Photographs of certain of the grades are shown 
in Plate 1, A and B. 
GRADES OF OTOCEPHALY 
In grade 1 the only obvious defect is more or less reduction of the lower 
jaw. In grade 2 no mandible can be felt externally. In grade 3 the ears 
are connected under the throat by bare skin. In grade 4 there is only a 
single median ear opening on the throat. In grade 5 the mouth and 
upper incisors are lost. In grade 6 the nostrils fuse. In grade 7 the 
eyes are in contact below a narrow nasal proboscis or are more or less 
fused. This fusion is complete in grade 8. The proboscis is lost in 
grade 9, the eye in grade 10, and the ear opening in grade n. Two 
small ears are the only externally visible organs of the head left. In 
grade 12 the body rounds off in front of the shoulders, with no sign of a 
head except a single small median external ear. This is the most ad¬ 
vanced grade which has been found. 
The internal anatomy has been studied to a considerable extent in the 
various grades, but will not be described in detail in this paper. It 
may be said, however, that all the changes from grades 1 to 4 are appar¬ 
ently consequent on reduction in Meckel's cartilage. In grade 4 the 
mandible is a short, flat crescent of bone firmly united to the reduced 
tympanies and hence to the upper part of the skull. The zygomatic 
arches are in contact or more or less fused posteriorly. The ear ossicles 
are fused and concealed by the reduced mandible. There is a mouth 
cavity, bounded ventrally by a mass of muscle in place of the lower jaw. 
The pharynx is necessarily very narrow in passing between the upper 
part of the skull above and the fused zygomas, and the fused ear ossicles 
and reduced mandible below. It expands posteriorly into the single 
middle ear. Posterior to this a swelling in the floor represents the tongue. 
A new series of changes begins with grade 5, in which the zygomas 
fuse anteriorly as well as posteriorly and the tooth-bearing portion of 
the maxillaries is lost. The cause is probably arrested development in 
the fronto-nasal process. Beginning with grade 6, changes in the brain 
become well marked. The cerebral hemispheres fuse in grade 6, though 
retaining about the normal shape and size. The fusion spreads back to 
the optic chiasma in grade 8, and there is continually increasing reduc¬ 
tion in size of the fore-brain sac relative to the cerebellum in grades 7, 
8, 9, and 10. The median optic nerve of grades 8 and 9 is lost in 
grade 10. In the specimen of grade 11 which was examined nothing 
was left of the brain but the medulla. The skull was reduced to a fairly 
normally shaped but undersized occipital ring posteriorly and normally 
sized but distorted periotic capsules anteriorly, with four minute flat 
bones (interparietal, parietals, fused frontals) between the latter. The 
persistence of the parts of the inner ear—cochlea and semicircular 
canals—is noteworthy. The fenestrae, however, were found to be absent 
in all specimens in which the ear ossicles were fused—that is, in some 
specimens of grade 3 and all of higher grades. The body ordinarily is 
plump and apparently normal, even in the most advanced grades. No 
internal abnormalities have been found in the body. 
