242 Prof. A. Macalister. Notes on the Varieties and 



eight weeks old, I found a bony centre on the right side, in front of 

 the nasal plate of the maxilla, bat none on the left. In a second of 

 the same size, both had begun to ossify, while in a ninth week 

 foetus I found no trace of bony growth. In nine other foetuses of 

 eighth week age, I found the traces of beginning ossification on both 

 sides in the form of single bony centres, which begin in the mem- 

 brane overlying the ethmoidal cartilage, and lying at the back of the 

 lachrymal duct, which has a distinct lumen by this time. 



At or near the end of the third month in foetuses of 6-7 centims., the 

 portion contiguous to the orbital plate of the maxilla is ossified, but 

 does not touch any of the developing bones around, except behind 

 and below the lachrymal grooves. In foetuses of the end of the 

 fourth month, the lower border is fully ossified, and forms a suture 

 with the maxilla ; ossification has also extended rapidly upwards, so 

 that the upper margin touches the frontal. The crista is developed, 

 and the orbital surface behind it is narrow, overlying the orbital 

 face of the ethmoidal cartilage, in which the first bony nodule does 

 not appear until the beginning of the thirteenth week. At this 

 period, the lachrymal bone is somewhat trigonal, and measures 3'5 

 to 4 millims. long (average of eight), and in one of my specimens the 

 hamulus has begun to ossify even at this age. Bony growth extends 

 more rapidly upwards and forwards than backwards, and the lachry- 

 mal part of the bone is completed, except at the two ends, by the 

 end of the fifth month, when as yet the orbital part is comparatively 

 narrow. Even at this stage, the anterior part is generally much 

 foraminated (fig. 1), and, while in contact with its other environing 

 bones, it has not yet touched the bony os planum (figs. 6, 7), nor the 

 maxillo-turbinal cartilage. The lowest part of the former is reached 

 at the end of the fifth or very early in the sixth month, when the 

 bone attains a length of 4'5 millims. In the sixth month, it has 

 extended further back, and has increased in length to 5 millims. ; in 

 the seventh, it has attained nearly its adult shape, and it averages 

 6 by 3 ; in the eighth, all the margining sutures are established, 

 except the lachrymo-ethmoidal, where there is still for the upper 

 two-thirds an area of uncovered cartilage, and also for a short extent 

 anteriorly and superiorly. The bone is now 6'25 by 4 millims., has 

 attained its adult shape, and in half my specimens has a developed 

 hamulus. In the ninth month, the average size is 7 - 5 x 5 millims., 

 but there is yet an angle of cartilage above and behind unfilled. The 

 hamulns is often fully ossified even to its facial part ; indeed, I have 

 seen this state attained in one foetal skull of eight months. 



The owimlum canalis naso-lachrymalia is early in its appearance. 

 In one eighth month skull I found it distinctly ossified, and in six 

 skulls of ninth month foetuses. The ossiculum infraorbitale I once 

 saw in a seven months skull. 



