Development of the head skeleton and pectoral girdle of salmons, with a note on the scales

Abstract

The bones of the head and pectoral girdle of species of Salmo and Oncorhynchus are described in terms of time of first ossification and later development. The development of the lateral-line system of the head is included as a part of the story of skeletal development. A series of arbitrary stages (I–X) is described and these stages are compared one with another and with the adult condition in Salmo. An underlying assumption is that developmental facts are useful in determining homologies. This is a work of comparative anatomy; it stresses a need for understanding homologies rather than being a defense or expansion of an established set of bone names or anatomical interpretations. Homologies are important as they have potential value in systematics. The names used for bones are generally acceptable to ichthyologists but the gist of the argument is that some names need to be changed to agree with those of tetrapods.