•2.')S DR A. J. WHITING ON THE 



of a remarkably thick muscular layer. Conspicuous within the hilar sheath are numerous 

 large nerve trunks. Sometimes a nerve may be seen to run alongside of or within a 

 trabecula, unaccompanied by any vessel. 



In the spleen of the Sheep the general arrangement is similar to that in the pig and 

 ox, but the muscular bundles are usually more loosely arranged than in them, and the 

 microscopic trabeculse are less strongly developed than in the ox, but more strongly than 

 in the pig. 



In the Dog the tunica propria is composed of two nearly equal portions. The outer 

 half consists of interlacing bundles of white fibrous tissue containing numerous con- 

 nective tissue corpuscles and elastic fibres with a few lymphoid cells. The inner' half 

 is composed of unstriped muscle mostly arranged in two layers, the outer of which is 

 transverse and the inner longitudinal. In the spleen of the puppy muscular fibre cells 

 are sparse, and occur only in the deeper part of the capsule. The trabeculse, which 

 are almost entirely muscular, are both numerous and large, but in the puppy they are 

 much less numerous. The majority of them are tunnelled by veins. The artery is 

 immediately surrounded by a somewhat thick layer of fine connective tissue, outside 

 which is a strong cylindrical sheath of muscle. 



In the Cat the greater proportion of the tunica propria consists of unstriped 

 muscle, externally there is merely a thin layer of white fibrous tissue. Most of the 

 muscle fibres are arranged transversely, so as to form a circular coat, but above as well 

 as below this there are a few strands of longitudinally arranged fibres. The trabeculse, 

 which are strongly developed, spring from the thick circular layer of the capsule, and 

 are composed almost entirely of muscle. The hilar sheath is also well developed (Plate I. 

 fig. 1). Its outer muscular layer is the thicker. Shortly after the artery has passed 

 through the hilus, its loose connective tissue sheath, derived from the inner layer of the 

 hilar sheath, contains a few lymphoid cells. In the newly-born kitten the capsule has 

 no distinct muscular layer, and the trabeculse are small and sparse. 



In the Narwhal the tunica propria is composed of two layers ; a superficial thicker 

 layer consisting of wavy bundles of white fibrous tissue with many elastic fibres 

 scattered at intervals, and a deeper thinner layer consisting chiefly of non-striped 

 muscle. There are no true trabeculse. Usually the veins are immediately surrounded 

 by the parenchyma, but occasionally there may be seen a few strands of unstriped 

 muscle supporting the larger veins. The vessels are accompanied into the interior of 

 the organ by a large amount of fibrous tissue, containing in its meshes numerous 

 lymphoid cells. Towards the periphery of the hilar sheath, unstriped muscle fibre cells 

 may generally be observed, among which there may sometimes be seen triradiate muscle 

 fibre cells similar to those found in the urinary bladder of Amphibia. 



In the Porpoise the tunica propria is much thicker on the side that corresponds 

 with the concave or hilar surface of the spleen. On the convex surface it may be 

 roughly divided into two layers : a superficial layer composed of white fibrous tissue, and 

 a deeper layer composed almost entirely of unstriped muscle. On the hilar surface it 



