iMi> Prof. A. Macalister. Notes on the Varieties and 



end was crossed by a bridge of mucous membrane subdividing it 

 into two. 



In man, ossification commences in the membrane behind and 

 internal to the lachrymal sac and duct independently of the ossifica- 

 tion in the bridge of tissue overlying the tube. The former gives 

 rise to the lachrymal bone, the latter to the nasal process of the 

 maxilla. 



The development of the bony environment of the sac is, however, 

 variable among mammals, and three distinct types are met with : 

 1st, that in which the pre- and post-lachrymal ossification are continu- 

 ous, and the bone forms a complete girdle for the nasal duct and a 

 large element of the interorbital region of the face ; 2nd, that in which, 

 while still engirdling the lachrymal sac, the bone is reduced to a 

 small thin lamella ; and Srdly, the form in which the lachrymal bone 

 is confined to the post-lachrymal region. 



The first form is met with among the lower and more generalised 

 mammals. In all the Didelphia it is thus large, and has a wide 

 lachrymo-jugal suture, larger in the carnivorous than in the herbi- 

 vorous forms, but in none excluding the maxilla from the frontal. 



Among the Ungulates the bone is large, with a large facial region. 

 In many it has a large lachry mo -nasal suture, and excludes the maxilla 

 from the frontal superficially. This is the case in Rhinoceros, Hippo- 

 potamus, many pigs, horse, Bos, Oreas, Tragelaphus, and many 

 Artiodactyles, but there is a maxillo-frontal suture in Hyrax, some 

 pigs, camels, Hyaemoschus, &c. In the pig there are often accessory 

 lachrymal ossicles in the lachrymo-frontal suture. 



Among all these the lachrymal tends to ankylose with the frontal 

 and malar, not with the maxilla. The same large form exists 

 through the Edentata and Sirenia, and a smaller form of the same 

 kind among the Rodents. The chief variation among these last is 

 the presence or absence of a jugal contact. There is a lachrymo- 

 jugal suture among the Sciuromorphs and Myomorphs, and a few of 

 the Hystricomorphs, such as Lagostomus, but it is generally absent 

 among the other porcupine allies, owing to the shortening of the 

 malar, not to any great alteration in the lachrymal, which in most 

 Rodents has a larger facial than orbital surface, though not much of 

 either. The Elephant, rodent-like in all its features, agrees with the 

 Hystricomorphs in this. 



Among Carnivores the lachrymal is small, forms but a small incon- 

 spicuous element of the orbital margin, and from its condition of 

 moderate size among Cynoids diminishes both towards GEluroids and 

 Arctoids, but especially towards the latter, among whom it appears 

 as a very small lamina. It becomes still smaller among Pinnipeds, 

 appearing in some like Callocephalus and Halichoerus as an exceed- 

 ingly slender, often scarcely ossified, detached scales, which is lust in 



