FEEDING 



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Figure 144. Transverse 

 ridges and papillae on the 

 baleen wall of a lo-foot Fin 

 Whale foetus. They are the 

 first rudiments of the baleen. 



smooth and flat gums, which, however, very soon give rise to two longi- 

 tudinal, fairly wide ridges on either side of the palate, the so-called baleen 

 ridges. In ten-foot embryos of Blue and Fin Whales, the centre of each 

 ledge then throws up an ever larger number of little walls at right angles to 

 the ledge. While the walls spread forward and backward from the centre, 

 small rows of papillae are formed at their extreme edges and soon develop 

 a hairy appearance. The wall - or lamella as it is called - with its papillae 

 is the original baleen (see Fig. 144). 



In cross-section, every papilla is seen to consist of an epidermal fold 

 outside a dermal fold made up of connective tissue, blood vessels and 

 nerves. The epidermis then becomes cornified towards the outside, thus 

 turning the round papilla into a cornified tubule (Fig. 145). While the 

 epidermis is made up entirely of a number of layers of living cells at its 

 base, it becomes progressively more cornified in the upper regions of the 

 papilla, until the entire wall of the top of the papilla consists of horn. The 

 reason why the 'hair' is a tubule rather than a solid pipe is explained 

 by the fact that the uppermost cells do not become cornified but die off. 

 In the layers of living cells, cell division takes place mainly longitudinally, 

 so that the papilla keeps growing in length rather than breadth. In adult 

 Mysticetes, the papilla itself is somewhat shorter than the part of the baleen 

 surrounded by gum (see below). In other words, in this region, the baleen 

 itself is still partly made up of living tissue, in the same way that, say, the 

 hoof of a horse (whose structure is analogous to baleen) consists of part- 

 living tissue as well. However, the visible part of the baleen consists 

 exclusively of hollow tubules with cornified walls. The tubules are packed 

 together without any connective tissue, so that they can shift with respect 

 to one another, which, as we have seen, makes the baleen particularly 

 elastic and pliable. 



A longitudinal section through the palate will reveal the way in which 

 the cortical layer is constructed (Fig. 145). It appears that the space 

 between any two walls or lamellae, each of which bears four rows of 



