QUARTERLY CHRONICLE. 101 



The absence of the nervi-nervorum on the sheath of the 

 primitive fasciculi explains to us their absence from certain 

 large nerve- branches. The tubes which compose them are 

 remarkable for their extreme tenuity. Each of them, how- 

 ever, is composed of an envelope, of a medullary layer and of 

 a cylinder axis. The optic nerve possesses two fibrous enve- 

 lopes ; 1st. A very thick external envelope, which extends 

 from the optic tract to the globe of the eye, and which con- 

 stitutes for this last organ a sort of ligament; 2nd. An 

 internal envelope which is very fine, and from which septa 

 are given, which dividing, and subdividing, and uniting one 

 with another, form longitudinal canals, all of about the same 

 diameter. This second envelope, which has the same relation 

 to the optic nerve as has the neurilemma to other nerves — 

 receives not the smallest'nervous twig. The external envelope, 

 on the other hand, receives a great number which take their 

 origin from the ciliary nerves. These nervi-nervorum of the 

 external sheath run at first in the superficial layers, where 

 they form an irregular plexus, and send off a few branches to 

 deeper layers. The external sheath of the optic nerves, so 

 rich in nervi-nervorum, is remarkable also for the abundance 

 of the elastic fibres, which enter into its formation. It was 

 formerly very erroneously considered as a uniting link 

 between the dura mater and the sclerotic. It differs, however, 

 from both; 1st. By its elastic fibres which are deficient in 

 both ; 2ud. By its nervi-nervorum, which are of an extreme 

 rarity in the cranial dura mater, and of which no vestige is 

 seen in the sclerotic. The anatomical analysis, therefore, 

 far from confirming the analogy which so many anatomists 

 believed to exist, attests that this part on the contrary is 

 distinguished from the two membranes with which it is con- 

 tinuous by characters which are peculiar to it. 



" Pulmonary Epithelium," by C. Schmidt. Thesis at 

 Strasbourg, 1866. A notice of this memoir, which appears 

 one of some value, is given. The conclusions of the author 

 are — 1. In the three classes of Vertebrates (fishes, reptiles, 

 mammals), the whole extent of the respiratory apparatus is 

 lined by an epithelial membrane. 2. The trabeculse in the 

 reptiles, and the bronchia in the mammals, are clothed with 

 a cylindrical vibratile epithelium. 3. The terminal parts of 

 respiratory apparatus (vesicles, alveoli, aerial cells) in which 

 the exchange of gases between air and blood takes place, are 

 lined with a simple pavement epithelium, without vibratile 

 cilia. 4. The passage from vibratile epithelium to pavement 

 epithelium takes place gradually. The last divisions of the 

 bronchia possess only pavement-cells, not vibratile. 5. The 



