152 SUMMARY OF CURRENT RESEARCHES RELATING TO 



outer world. In bony fishes the ductus endolymphaticus is quite 

 different, and arises at a late stage as a constriction of part of the 

 alveus. Its growth in length takes place from above downwards, by a 

 division of the cells of its walls. In Anura the duct is formed as in 

 Teleosts, and has nothing to do with that of Selachians. The formation 

 of the semicircular canals is quite similar in Salmo and Pelobates. 



Organ of Jaco.bson in Fcetai Cat.* — Helene Steinberg finds that 

 in the foetus of the cat in the second half of the gestation, the organ 

 of Jacobson has the form of an epithelial canal, ending dorsally in a 

 cul-de-sac. It is enveloped in a hyaline cartilaginous skeleton, inde- 

 pendent of the nasal skeleton. This capsule is incomplete for the 

 greater part of its length, and forms a gutter at the bottom of which 

 the epithelial canal lies. The organ has two tunics, epithelial and con- 

 nective. In the mid-region of the organ, the median wall is formed 

 by a thickened epithelium resting on a connective mucosa, and the 

 lateral wall consists of a delicate epithelium, supported on a fibrous 

 dermis, very vascular and very richly innervated. 



; h. Histology. 



Relation of Muscle-fibrils to Tendon-fibrils.t — W. M. Baldwin 

 has studied this in the striped muscles of tadpole, frog, chicken, mouse, 

 and calf. In the manner of termination of muscle-fibres, two general 

 types may be recognized, one in which the long axes of the tendon- and 

 of the muscle-fibres coincide, and one in which they meet at an angle. 

 In neither of these two types are the muscle-fibrillse in continuity with 

 the tendon-fibrillse. 



Developing muscle-fibres terminate in a number of cone-shaped 

 processes of sarcolemma, to the apex of which a tendon-fibril is attached. 

 In the adult, the muscles conforming to the first type mentioned above, 

 preserve the apical processes of their sarcolemma end. In the adult, 

 these processes of sarcolemma are dovetailed into the tendon end. The 

 sarcolemma at the tendon end of such muscles is not markedly thickened. 



The central tendon of bipenniform muscles-- the second type men- 

 tioned above — is invested by a connective-tissue sheath or periten- 

 dinum, which consists of connective-tissue fibres and cells, and separates 

 the tendon-fibrillse from the muscle-fibres. On muscles conforming to 

 the second type of structure, the sarcolemma end presents a Hat surface 

 which rests directly against the attached structure, be it peritendinum, 

 perichondrium, or periosteum. This sarcolemma end is considerably 

 thickened, and is composed of a homogeneous substance. It presents a 

 number of sarcolemma projections which intrude into the substance of 

 the muscle-fibre. These projections are derived from the fused adjacent 

 walls of the cone-shaped processes of the sarcolemma which weje present 

 at an earlier developmental stage of the fibre. The muscle-fibrillae in 

 adult muscles of this second type preserve their features of cross-striation 

 up to the sarcolemma. This sarcolemma end is not perforated either 

 by the tendon-fibrillje, the peritendinum-fibrillae, or the muscle-fibrillae. 



* Anat. Anzeig., xlii. (1912) pp. 466-72 (2 figs.) 

 t Morphol. Jahrb., xlv. (1913) pp. 249-66 (1 pL). 



