OCR Text |
Show 580 DR. J. SYMINGTON ON THE [NOV. 17, columnar epithelial cells next the free surface such as are generally found. It is possible that these have been detached. In the Guinea-pig, Dog, and Rabbit Dr. Klein found the organ of Jacobson to be flattened from side to side with the outer wall pushed slightly inwards, so that on transverse vertical section the organ was kidney-shaped. The outer wall was covered with ciliated columnar epithelium, while the inner wall possessed, in addition to ordinary columnar cells, special sensory cells. The outer wall of the organ in these mammals evidently corresponds to that covering the turbinated process in the Ornithorhynchus, while the inner wall is represented by the structures lining the general cartilaginous capsule. In all mammals so far as at present investigated, except the Monotremes, the cavity of Jacobson's organ communicates anteriorly with the nasal chamber or with Stenson's duct, and this opening is anterior to the cavity of the organ. W e have already seen that this is not the case in the Ornithorhynchus, where the cavity extends forwards as well as backwards from its opening into Stenson's duct. In Lizards the duct from Jacobson's organ passes backwards and downwards to open into the cavity of the mouth. The cavity of the organ of Jacobson in the Ornithorhynchus is about 5 to 6 m m . in length. Both extremities end blindly, the posterior one just in front of the hinder end of the dumb-bell-shaped bone. The ridge on the inner wall of the nose caused by Jacobson's organ is prolonged backwards nearly 3 cm. beyond the termination of the organ proper. The ridge here consists of glandular tissue and bundles of olfactory nerve-fibres, the nerves being internal to the glandular tissue (see fig. 3, Plate XLIIL). The nasal cavity is lined by stratified squamous epithelium until near the posterior end of Jacobson's organ, where it becomes gradually replaced by columnar epithelium. A transverse vertical section of the nose (see fig. 3, Plate XLIIL) about 1*5 cm. behind the nostrils shows that the walls of the nose are still mainly cartilaginous; the floor, however, contains the palatine process of the superior maxillary bone, and the lower part of the nasal septum the vomer. The Dumb-bell-shaped Bone. Since 1879, when Professor Albrecht (3 a) published his first paper dealing with the ossification of the inter-maxillary bone, there has been a vigorous controversy as to whether this bone is normally developed in man and the higher mammals from one or two centres. The embryological evidence in favour of two centres appears to me to be unsatisfactory, the careful observations of T. Kolliker (18) and Schwink (17) being strongly in favour of its formation from a single centre. Albrecht's (3) views as to the morphology of the dumb-bell-shaped bone in the Ornithorhynchus have, however, been pretty generally accepted. He directed attention to the fact, previously noticed by Rudolphi, Meckel (1), and Owen (2), and since confirmed |